On March 1, 2000, 09:51:37 UT Earth-crossing time, a GRB was detected
by ASM, Ulysses and NEAR.
- GCN notice #568
D. A. Smith (MIT) reports on behalf of the ASM team at MIT and
NASA/GSFC, and K. Hurley (UCB) and T. Cline (NASA/GSFC) report on
behalf of the Ulysses and NEAR GRB teams:
The ASM has detected a GRB at 03/01/2000 09:51:37 (UTC). The burst
showed a single peak with a simple fast-rise, slow-decay structure.
The three ASM energy channels showed the strongest response in the
5-12 keV band, reaching a peak flux of 3.7+-0.7 Crab (5-12 keV) in 1-s
time bins. The event lasted approximately 10 seconds. The event was
detected by a single ASM SSC, yielding an error box (90% confidence,
including systematic and statistical error) 4.2 degrees long and 8.7
arcminutes wide, centered at R.A. = 16h 13m 14s and Decl. = 28o 37'
59.2" (J2000.0), with a position angle of -117.1 degrees.
Ulysses and NEAR observed this burst. Preliminary triangulation gives
an annulus 5' in full-width (3 sigma), centered at R.A. = 20h 34m
7.56s and Decl. = 20o 32' 19.62s (J2000.0), with a central radius of
57.520 degrees. This annulus may be refined.
This annulus intersects the ASM error box at near-right angles to
create a composite localization of a parallelogram of area ~50
sq. arcmin with the following corners (J2000.0):
R.A. Decl.
16h 20m 30s +29o 30' 14.3"
16h 20m 08s +29o 27' 50.4"
16h 20m 13s +29o 19' 40.8"
16h 20m 35s +29o 22' 00.0"
Figures and charts can be found at
http://gx339.mit.edu/grb000301c/.
- GCN notice #570
J. P. U. Fynbo (U. Of Aarhus),
B. L. Jensen, J. Hjorth, H. Pedersen (U. of Copenhagen) and
J. Gorosabel (DSRI, Copenhagen)
on behalf of a larger European GRB Consortium report:
Using the ALFOSC on the 2.5m Nordic Optical Telescope, we have
obtained I, R, B, and U-band imaging of the field of GRB 000301C
(Smith et al., GCN #568) on 2000 March 3.14-3.28 UT. Comparing with
DSS-2
plates we find an object which is notoriously absent from DSS-2
(red) and (blue).
The coordinates of this object are:
RA(J2000) : 16 20 18.6
Dec(J2000) : +29 26 36
(with an uncertainty of about 1")
This object is detected in individual exposures of 900s,
in all four colors.
Preliminary USNO-A1.0-based magnitude is: R~20.3 +- 0.5 .
The object appears bluer than most GRB OTs observed so far.
Sections of the images will be made available at:
http://www.astro.ku.dk/~brian_j/grb/grb000131c
along with a DSS-2 finding chart.
- GCN notice #571
S.Bernabei, S.Marinoni, C.Bartolini, A.Guarnieri, A.Piccioni,
Astronomical Observatory and Astronomy Department, Bologna University, and
N.Masetti, ITeSRE-CNR, Bologna report:
A preliminary quick inspection of one single R image of the field of
GRB 000301C (RXTE/ASM and IPN localization, Smith, Hurley and Cline, GCN 568)
taken on March 3, starting at 04:27 UT (EEV-CCD,1000 sec exposure) with the
152 cm telescope of Loiano shows an object located at RA=16h 20m 18.5s,
D=29`26'35" (Eq. 2000), which is not present on the Digital Sky Survey.
It is roughly 1 mag brighter than the POSS limit and it is coincident with
the object detected by Fynbo et al., GCN 570.
Only new observation can decide if this object is the OT connected with
GRB 000301C.
- GCN notice #572
B. Stecklum, S. Klose (Thueringer Landessternwarte Tautenburg),
O. Fischer (Universitaets-Sternwarte Jena),
C. Bailer-Jones, U. Thiele, A. Aguirre
(Max-Planck-Institut fuer Astronomie, Heidelberg),
F. J. Vrba, A. A. Henden, C. B. Luginbuhl,
B. Canzian, S. E. Levine, H. H. Guetter, J. A. Munn
(U.S. Naval Observatory, Flagstaff),
D. H. Hartmann (Clemson University, Clemson),
A. Castro-Tirado (LAEFF-INTA, Madrid, and IAA-CSIC, Granada),
J. Greiner (AIP Potsdam), and
J. Gorosabel (LAEFF-INTA, Madrid, and University of Amsterdam)
report:
The error box of the burst GRB 000301c reported by Smith et al. (GCN
#568) was imaged with the Calar Alto 3.5-m telescope on March 3, 4:41 UT
- 5:38 UT using the near-infrared camera Omega Cass. The frames
were taken in the course of a project whose goal is to measure the
degree of linear polarization of GRB afterglows. The limiting
magnitude of the K'-band image is about K'=19 after adding all images
taken at different position angles of the wire-grid polarizer.
The potential optical transient reported by Fynbo et al. (GCN #570) is
clearly detected. Based on the assumption that the B-R colour index of
the star USNO 125_07686794 is representative for its spectral type, a
preliminary estimate of the K'-band magnitude of the potential afterglow
of 17.4 was derived.
The image is posted on the Tautenburg Web page at
http://www.tls-tautenburg.de/research/grb000301c.html.
- GCN notice #573
P. Garnavich (Notre Dame), P. Barmby, S. Jha, K. Stanek (CfA) report:
We imaged the ASM error box (GCN 568) of GRB000301C with the
FLWO 1.2m telescope and R-band filter on 2000 Mar. 3.51 (UT)
and detect the optical candidate reported by Fynbo et al. (GCN 570).
Using Landolt standards taken during the night, we find
a preliminary magnitude of R=20.28 +\- 0.05 mag. This is
very close to the Fynbo et al. estimate taken some 7 hours
earlier. However, given the quoted errors for the two measurements
there is room for some variability over this time. Further
observations are needed to confirm this source as the GRB
afterglow.
We have calibrated the following stars in R to use as comparisons:
star Offset East Offset North R
A -6" -1" 18.05 +/- 0.05
B -4 -89 18.48
C 70 -55 18.62
D -7 62 17.04
Offsets are in arcsec from the GRB candidate
with positive offsets east and north.
- GCN notice #575
Christian Veillet reports:
The candidate for the optical transient (OT) associated with the gamma ray
burst
GRB000301c has been observed in imaging mode with MOS on the 3.6-m CFH
Telescope
in the course of the French GRB follow-up program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
Relative photometry in B and R with respect to the reference star A (GCN #573)
is as following:
delta B = 1.29 +/- 0.05 2000 March 3.50 (UTC)
delta R = 2.19 +/- 0.05 2000 March 3.51 (UTC)
The R magnitude inferred from star A magnitude determination in GCN #573
is 20.24 +/-.07, in good agreement with the GCN #573 value of
R = 20.28 +\- 0.05 measured at the same epoch.
B and R images can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html
B calibrations will be made tonight if no multicolor photometry is made
available
for reference stars in the field.
D. Elbaz and H. Flores are acknowledged for their help in these observations.
- GCN notice #576
J. P. U. Fynbo (U. of Aarhus),
B. L. Jensen, J. Hjorth, H. Pedersen (U. of Copenhagen),
J. Gorosabel (DSRI, Copenhagen)
on behalf of a large European GRB Consortium report:
In response to Garnevich et al., (GCN #573), we have
carried out photometry of stars A-D of GCN #573
and of the OT proposed by Fynbo et al., (GCN #570).
This photometry has been performed on our combined
2000, March 3, 3x900s NOT R-band image of the GRB-field.
Using the stars A-D of Garnevich et al.
as reference, we derive an R-band magnitude for the OT
at UT_mean = March 3.17 of R = 19.94+-0.04.
Hence, the candidate OT is fading and we thus propose
it as being the optical counterpart to GRB 000301C.
The implied power-law decay index from this magnitude
and the magnitude measured by Garnevich et al.
is rather steep : -1.8
(with this rate, a magnitude of R:20.8 is predicted for
March 4.17 UT).
- GCN notice #577
Naoto Kobayashi (Subaru Telescope, National Astronomical Observatory of Japan),
Miwa Goto, Hiroshi Terada (Kyoto University),
Alan T. Tokunaga (Institute for Astronomy, University of Hawaii),
on behalf of SUBARU Telescope team and SUBARU IRCS team
On 3 March, 12:48 UT - 13:54 UT, we observed the candidate optical
counterpart to GRB 000301C that was reported by Fynbo et al. (GCN
Circular #570). We used the Subaru 8m Telescope on Mauna kea with a
new instrument IRCS (Infrared Camera and Spectrograph for the Subaru
Telescope) during its first engineering run. Near-infrared J,H,K'
filters were used. The candidate optical transient (OT) was clearly
detected in all three bands.
We have performed preliminary photometry with 2-arcsecond aperture
using Persson standards taken during the night. The resultant magnitude
of the candidate OT was K'=17.6+-0.1 mag. For reference, the magnitude
of the near-by star, USNO 125_07686794, was estimated at K'=16.0+-0.05
mag.
Comparing to the estimated K' magnitude of 17.4 (at 4:41 UT - 5:38 UT)
reported by Stecklum et al (GCN Circular #572), our photometry may
suggest that the brightness decreased by roughly 0.2 mag during 8
hours. However, given the possible systematic errors for the two
estimates (e.g., photometric system is different), further
observations are necessary to confirm this OT candidate as the GRB
afterglow.
- GCN notice #578
J. P. Halpern, N. Mirabal, & S. Lawrence (Columbia U.) report
on behalf of the MDM Observatory GRB follow-up team:
We imaged the location of GRB 000301C as determined by the
intersection of the RXTE All-Sky Monitor error box and the
Ulysses/NEAR annulus (Smith, Hurley, & Cline, GCN #568)
in the R band on March 3.51 UT using the MDM 1.3m telescope.
The optical transient found by Fynbo et al. (GCN #570,576)
is measured at R = 20.24 +/- 0.05, referenced to the comparison
stars of Garnavich et al. (GCN #573). This is consistent
with measurements by Garnavich et al. and Veillet (GCN #575)
that were obtained contemporaneously. The implied power-law
decay index is still rather uncertain. Using our magnitude
and that measured by Fynbo et al. (GCN #576), we find
alpha = -1.56 +/- 0.30. This predicts R = 20.90 +/- 0.18
on March 4.51 UT.
We measure the position of the optical transient to be
(J2000) RA 16:20:18.550, Dec +29:26:35.96 relative to
30 USNO-A2.0 stars having a dispersion of 0".31 in radius.
CCD images are posted at
http://www.astro.bio2.edu/grb/
- GCN notice #579
Alberto J. Castro-Tirado, IAA-CSIC (Granada),
Holger Bock, Landesternwarte (Heidelberg),
Jochen Greiner, AIP (Potsdam),
Sylvio Klose, TLS (Tautenburg),
Jose M. Castro Ceron, ROA (San Fernando),
Javier Gorosabel, DSRI (Copenhagen),
on behalf of a larger European GRB collaboration report:
We have just obtained a 15-minute R-band exposure centred at
the GRB 000301C error box (Smith et al. GCN#568) starting at
01:15 UT on 4 March 2000 with the 1.23 m telescope at the
German-Spanish Calar Alto Observatory (CAHA).
Using the stars A-D of Garnavich et al. (GCN #573) we derive
R = 20.46 +/- 0.09 for the optical counterpart reported by Fynbo
et al. (GCN #570). When combining this value with the measurements
by Fynbo et al. (GCN #576) and Halpern et al. (GCN #578) the
power-law decline exponent becomes alpha = -1.27 +/- 0.20.
- GCN notice #580
Frank Bertoldi (MPIfR Bonn) reports:
The likely afterglow of GRB 000301C (Smith et al., GCN 568) was
detected at 250 GHz (1.2 mm) with the 37 channel Max-Planck Millimeter
Bolometer (MAMBO) array (80 GHz bandwidth, 10.7 arcsec HPBW) at the
IRAM 30 m telescope on Pico Veleta, at the position reported by Fynbo
et al. (GCN 570) and Halpern et al. (GCN 578). The object was
observed on 4 March 2000 from UTC 7 to 11:30, in standard on-off mode,
under good weather conditions (stable atmosphere with opacity slowly
rising from 0.21 to 0.26), and good pointing accuracy (<2"). The
total on plus off target integration time was 7800 seconds.
A source is clearly detected with flux density
f(250 GHz) = 1.9 +- 0.3 mJy
We hope to continue monitoring its flux.
- GCN notice #581
P. Garnavich (Notre Dame), P. Barmby, S. Jha, K. Stanek (CfA) report:
We again imaged the candidate optical counterpart of GRB000301C
with the FLWO 1.2m telescope and R-band filter on 2000 Mar. 4.38 (UT)
and estimated its magnitude based on the calibration stars
given in GCN 573. We find R=20.56 +/- 0.05 which suggests a rather
slow decline rate. Using the magnitude estimates from Veillet (GCN 575),
Fynbo et al. (GCN 576), Halpern et al. (GCN 578) and Castro-Tirado et al.
(GCN 579) we find the data best fit a single power-law index
of -1.07+\-0.13 . However, using data taken since Mar 3.5 (UT) gives
an even more shallow slope of -0.8 +\-0.2 and suggests a
possible flattening of the decay rate.
- GCN notice #582
J. P. Halpern, N. Mirabal, & S. Lawrence (Columbia U.) report
on behalf of the MDM Observatory GRB follow-up team:
We reobserved GRB 000301C in the R band on March 4.50 UT using
the MDM 1.3m telescope, measuring R = 20.61 +/- 0.04, referenced
to the comparison stars of Garnavich et al. (GCN #573).
The power-law decay derived from this and previous measurements
(GCNs #575,576,578,579) is slower than previously indicated.
We find alpha = -1.07 +/- 0.09. This predicts R = 20.95 on
March 5.50 UT.
The decay curve and a new CCD image are posted at
http://www.astro.bio2.edu/grb/
The figure has been updated
with more recent measurements than were
included in the fit described above.
- GCN notice #583
A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:
We have acquired preliminary UBVRcIc all-sky photometry for
the field of GRB000301C with the USNOFS 1.0-m telescope on one
photometric night. This 11x11arcmin field covers the IPN
error box, contains the proposed optical counterpart, and extends
fainter than R=20. The file includes the Garnavich, et. al.
(GCN 573) R-band comparison stars with similar magnitudes
within errors. We have placed the photometric data
on our anonymous ftp site:
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb000301c.dat.
This file will be updated as soon as the weather improves.
The current photometry has a potential external zero-point
error of about two percent. Negative errors are Poisson only;
positive errors are standard deviation of two or more measures.
The astrometry in this file is based on linear plate
solutions with respect to USNO-A2.0. The internal errors
are less than 100mas.
- GCN notice #584
M. Eracleous (Penn State), M. Shetrone (Mc Donald Obs.), S. Sigurdsson,
P. Meszaros (Penn State), J. C. Wheeler, and L. Wang (U. Texas)
on behalf of the Hobby-Eberly telescope GRB follow-up team:
We obtained a spectrum of GRB 000301C with the Low-Resolution
Spectrograph on the Hobby-Eberly Telescope on March 4.410. The
spectrum, which was taken under non-ideal weather and seeing
conditions, covers the range 4100-8000 A. We detect no obvious
emission or absorption features. The flux density per unit frequency
interval (f-nu) appears to increase monotonically toward the red.
- GCN notice #585
J. P. Halpern, N. Mirabal, & S. Lawrence (Columbia U.) report
on behalf of the MDM Observatory GRB follow-up team:
We also obtained B-band images of GRB 000301C on March 4.52 UT
using the MDM 1.3m telescope. By employing the Henden et al.
(GCN #583) photometry of the comparison stars A and D of
Garnavich et al. (GCN #573), we measure B = 21.41 +/- 0.04,
and we determine that B-R = 0.77 +/- 0.06 at this time.
Correcting for the Schlegel et al. (1998) Galactic extinction at
this location, A_B = 0.23 and A_R = 0.14, we find an intrinsic
B-R = 0.68 +/- 0.6, which corresponds to a spectral slope
beta = -0.87 +/- 0.14. This value, together with the temporal
decay slope alpha = -1.07 +/- 0.09 (GCN #581,582), is consistent
within the errors with the canonical alpha = (3/2)beta behavior
of a spherical afterglow in an uniformly dense medium.
Little intrinsic extinction is required to explain the color.
The B-band image is posted at http://www.astro.bio2.edu/grb/
- GCN notice #586
James Rhoads and Andy Fruchter (STScI) report:
We observed the proposed afterglow of GRB 000301c with the NASA IRTF + NSFCam
in K' band (2.1 microns) on March 4.640, and in J band (1.25 microns) on
March 4.652. The data were photometrically calibrated by observations
of UKIRT faint standard 27. Seeing was approximately 0.85" in K'
and 0.95" in J.
We find K'=17.65 +- 0.04 and J=19.10 +- 0.05 (statistical error only)
for the candidate afterglow. Aperture photometry was performed using a
0.9" (3 pixel) radius aperture, corrected to an effective aperture of
2.7" radius using aperture corrections derived from the brighter star
5.7" W and 1" S of the proposed OT. For reference, this star had
magnitudes K'=15.96 +- 0.02 and J=16.63 +- 0.01.
No correction was made for atmospheric extinction or color terms; however,
these are expected to be small. (The standard was observed at airmass 1.09,
and the GRB field at airmass 1.02.)
We detect a faint object, quite possibly a galaxy, approximately 2" N and
1" E of the candidate OT; this could be the host galaxy if the OT is
real. This object has approximate magnitudes K'=19.8, J=20.8.
This K' flux shows no significant decline from the earlier reported
observations (Stecklum et al, GCNC 572; Kobayashi et al, GCNC 577),
while it would be expected to decay by 0.44 magnitudes from Kobayashi's
data point for a t^-1.0 power law. This relative constancy of the near-IR
flux, despite optical fading, is difficult to reconcile with GRB afterglow
models, especially if it persists for more than a day.
We note that many classes of variable objects (other than
afterglows) show stronger variability at bluer wavelengths.
The weak or nonexistent variability in the K' filter is therefore
a cause for concern, and we urge continued followup at both optical
and IR wavelengths.
We thank the staff of the IRTF for help with these service observations.
- GCN notice #587
Naoto Kobayashi (Subaru Telescope, National Astronomical Observatory of Japan),
Miwa Goto, Hiroshi Terada (Kyoto University),
Alan T. Tokunaga (Institute for Astronomy, University of Hawaii),
on behalf of SUBARU Telescope team and SUBARU IRCS team
We report an improved near-infrared photometry of the proposed OT for
GRB000301C in our J,H,K' images taken with IRCS (InfraRed Camera and
Spectrograph) on the SUBARU Telescope on March 3.55 UT. Photometry was
performed on co-added image (18-min total exposure time) while quick
photometry of one K' frame (2-min exposure) was reported in GCNC #577.
Seeing was approximately 0.45" in K' and 0.50" in J/H throughout the
observation. The OT magnitudes were determined with about 0.01 mag
statistical accuracy in all bands.
Relative magnitudes of the OT to the near-by bright star (5.7" W and
1" S) were derived and compared to the results by Rhoads & Fruchter
(GCN #586) to examine possible near-infrared decay of the OT. The
results are as follows:
relative magnitude(OT-Star) Reference
J H K'
UT 3.55 March 2.27 2.18 1.56 this work
UT 4.64 March 2.47 ---- 1.69 GCNC #586
decay/day 0.20 ---- 0.13
Since we expect the uncertainty of relative photometry is quite small
(e.g., 0.01 mag), these results suggest that the OT is actually fading
in the near-infrared. The near-infrared decay rate is smaller compared
to the R-band decay rate (~0.4-mag/day) of the same period. The
slightly larger decay in J compared to K' may suggest that the decay
rate is smaller in longer wavelengths.
The possible host galaxy reported by Rhoads & Fruchter (GCN #586) is
also detected in our images. It looks slightly extended
(FWHM=0".6-0".7) in our K'-images of 0".45 seeing, which suggests
that this source is actually a galaxy.
- GCN notice #588
The candidate for the optical transient (OT) associated with the gamma ray burst
GRB000301c has been observed in imaging mode with MOS on the 3.6-m CFH Telescope
in the course of the French GRB follow-up program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
An R image has been taken with a good seeing (better then 0.8 arcsecond).
Relative photometry with respect to the reference star A (GCN573) using
GCN583 photometry is as following
R = 20.86 +/- 0.04 2000 March 5.63 (UTC)
It is significantly different from the prediction based on a temporal decay
slope alpha = -1.07 +/- 0.09 (GCB581) and seems to confirm the flattening
of the
decay rate suggested in the same circular. More data would be welcome though!
The relative photometry in B and R published in GCN575 becomes, using GCN583
data:
B = 21.11 +/- 0.04 2000 March 3.50 (UTC)
R = 20.27 +/- 0.04 2000 March 3.51 (UTC)
and B-R = 0.84 +/- 0.06 at the same date, to be compared with 0.77 +/- 0.06
on March 4.52 (GCN585).
D. Elbaz and H. Flores are acknowledged for their help in these observations.
- GCN notice #589 + #590
E. Berger (Caltech) and D. A. Frail (NRAO) report on behalf of a
larger collaboration:
Beginning on March 5.67 UT we used the VLA to observe a field centered at
the position of the optical transient reported by J. P. U. Fynbo, et al,
and S.Bernabei, et al (GCN 570 and 571). We detect a 300 microJy radio
source at 8.46 GHz, located at the position of the optical transient.
Absolute flux calibration is not yet available. Continued observations at
a broad range of frequencies are underway.
- GCN notice #591
S.G. Bhargavi and R. Cowsik
(Indian Institute of Astrophysics, Bangalore, India 560034) report:
We imaged the field of GRB000301c (GCN #568) using the 2.34m Vainu Bappu
Telescope at Kavalur, India from March 2nd to March 4th, 2000 with clear
sky conditions.
date UT filter & total exposure
-----------------------------------------------
2, Mar 22.46 -23.8 UT B(20min), R(45min)
3, Mar 22.08 -23.96 UT R(70min),I(45min)
4, Mar 21.23 -23.966 UT R(60min),I(30min),B(50min)
------------------------------------------------------
Since the internet is down I am unable to view the images reported
in various GCN circulars. However, referring to the offset positions of
reference stars by Garnavich et al (GCN #573) and a FAX of DSS picture
the object proposed to be the counterpart of GRB000301c
(GCN #570,576) is identified in all our images.
The data reduction is in progress.
- GCN notice #592
The candidate for the optical transient (OT) associated with the gamma ray
burst
GRB000301c has been observed in imaging mode with MOS on the 3.6-m CFH
Telescope
in the course of the French GRB follow-up program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
The R image mentioned in GCN588 has been examined for a possible detection
of the galaxy observed in the near IR (GCN586-587).
Nothing is detected at the reported position (1"E 2"N). The detection limit in
this area of the field is at R~25.
The OT itself has no significant elongation compared to nearby stars.
"Something" is detected at -1"E 2"N though. It was not visible on the
previous R image taken on March 3.5 due to a much poorer seeing (~1.5").
Its magnitude (if real) is 24.7 +/- .3 .
Should I add that more deep imaging is needed?...
Image available at
http://www.cfht.hawaii.edu/~veillet/grb.html
D. Elbaz and H. Flores are acknowledged for their help in these observations.
- GCN notice #593
A. Gal-Yam, E. Ofek, D. Maoz and E.M. Leibowitz, Wise Observatory, Tel Aviv
University, Israel, report:
Using the Wise Observatory 1-m telescope and the observatory new SiTe CCD
camera, we obtained on March 4 two 900 sec and one 1800 sec exposures through
an R filter, and one 1800 sec V exposure, of the GRB000301C OT candidate. The
mean UT of the 3 R exposures is March 4.0799. The weighted mean R magnitude,
measured relative to stars A-D of Garnavich et al. (GCN 573),
is 20.573 +/- .06. The UT of the V image is March 4.1121, and the OT-ref*
magnitude differences, with respect to stars A,B,C and D, are,
respectively (+/-0.12): 2.356, 1.635, 1.342 and 3.683.
- GCN notice #594
A. Fruchter and J. Rhoads (STScI) report:
The field of the presumed afterglow of GRB 000301C was re-oberved with
the NASA IRTF and NSFCam in the K' band (2.1) microns on UT March
5.61. We use our calibration from GCN 586 and comparison to the
brighter star ~6" to the W for photometry. We find that the presumed
OT is now fainter than the reference star by 2.04 mag, so that
K'=18.00. The formal error from photon statistics is 0.05 mag. The
total error on the relative magnitude might be as large as 0.07 mag,
and the total error on the absolute magnitude as large as 0.10 mag.
Relative photometry of five other sources in the field shows no
variation with respect to the bright star greater than 1.5 sigma.
The transient has therefore declined by 0.35 +- 0.08 mag in K' between
UT 4.64 March and 5.61 March. This is in contrast with a decline of
0.13 +/- 0.05 mags between 3.55 and 4.64 March (GCN 586 and 587).
The slow-down in the rate of decline in the R band over the same time
span (Veillet GCN 588) suggests a remarkable decoupling of the optical
and near-infrared behavior of this transient.
The candidate host is 1" W (not E as incorrectly reported in GCN 586)
and 2"N of the OT. It is the same object reported by Veillet in GCN
592. This galaxy has colors of order R-K'=5, J-K'=1; however, the
color must be considered highly uncertain until better comparison of
the optical and infrared images can be made.
- GCN notice #595
V. Mohan, A.K. Pandey, S.B. Pandey, R. Sagar, UPSO, Nainital and
Alberto J. Castro-Tirado, IAA-CSIC (Granada) report on behalf of a larger
European GRB collaboration :
We have observed the field of GRB 000301C on March 3 and March 5 using the
1-metre telescope of U.P. State Observatory and 2k x 2k CCD. The R magnitudes
calibrated using stars A and D of Garnavich et al. (GCN #573) come out to be
as follows:
Mar 3.93 UT 20.53 +/- 0.05
Mar 5.96 UT 21.18 +/- 0.05
Using all R band observations reported so far the value of alpha
comes out to be 1.02 while excluding the R magnitude reported in #GCN 588,
alpha comes out to be 1.12 +/- 0.1.
- GCN notice #596
James Rhoads and Andy Fruchter (STScI) report:
We observed the candidate counterpart of GRB 000301c for a third time
with the NASA-IRTF + NSFCam on March 6.595. The magnitude of the transient
relative to the reference star 6" west has decayed to +2.60 +- 0.12,
giving K'=18.56 +- 0.12 (statistical error only).
This is a decay of 0.56 magnitudes since our preceding observation (on
March 5.61 UT), and so the decay of the 2.1 micron flux continues to
accelerate. The K' band light curve is a considerably worse fit to any
power law than the R band light curve.
This unusual behavior warrants closer investigation, and further followup
at all wavelengths (especially the near-IR) is encouraged.
- GCN notice #597
R. Mujica, V. Chavushyan, INAOE; S. Zharikov, G. Tovmassian, OAN IA
UNAM, Mexico, report:
We observed GRB 000301C optical counterpart in the R band on March
4.458 UT using the 2.1m telescope of the "Guillermo Haro" Observatory in
Cananea, Sonora, Mexico with the Landessternwarte Faint Object
Spectrograph and Camera (LFOSC). Using reference stars A-D of Garnevich
et al. (GCN 573), we derive R-band magnitude of R = 20.54+\-0.06 for
the OT at 2000 March 4.458 UT. This magnitude is in a good agreement
with other observations that were obtained approximately at the same
time (GCN #581, 582, 593).
- GCN notice #598
The candidate for the optical transient (OT) associated with the gamma ray burst
GRB000301c has been observed in imaging mode with MOS on the 3.6-m CFH Telescope
in the course of the French GRB follow-up program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
The OT has the following magnitude, using star A (GCN573) photometry (GCN583):
R = 21.70 +/- 0.07 2000 March 7.65 (UTC)
This value does not fit very well with the the R magnitudes published in the
previous GCN, in particular by Mohan(595), if we assume a power law common
to all observations. In fact, the best fit of the data published so far is
obtained with a linear magnitude decay of 0.32 +/- 0.02 mg/day...
The acceleration in the decay in K (GCN596) seems also to be seen in R.
More data, as well as a careful reanalysis of the existing images, are
clearly needed!
The faint source found on March 5 (GCN592), recognized in GCN594 as identical
to the one detected in IR at NASA IRTF, is definitely there also
on the March 7 image. A composite of the two images is available at
http://www.cfht.hawaii.edu/~veillet/grb.html .
Its R magnitude is measured as 24.3 +/- 0.3 , to be refined with further
analysis.
S. Lilly is acknowledged for his help in this observation.
- GCN notice #599
S. Bernabei (Astron. Obs., Bologna), C. Bartolini, L. Di Fabrizio,
A. Guarnieri, A. Piccioni (Dip. Astronomia, Univ. of Bologna),
and N. Masetti (ITeSRE/CNR, Bologna) report:
We have imaged the proposed optical counterpart (GCN #570) of GRB000301C
(GCN #568) on March 3, 4, 6, 7 and 8, 2000, in the R band with the 152 cm
Loiano telescope (plus EEV CCD) of the Observatory of Bologna.
Using the R magnitudes of the four comparison stars quoted by Garnavich
et al. (GCN #574) we obtain the following figures:
Date exptime seeing R mag.
---------------------------------------------------
Mar. 3.191 1000 s 2".0 20.11 +- 0.05
Mar. 4.178 2200 s 3".0 20.22 +- 0.2
Mar. 6.145 1800 s 1".7 21.60 +- 0.2
Mar. 7.135 1800 s 1".7 21.63 +- 0.15
Mar. 8.157 1800 s 1".5 21.63 +- 0.1
The R magnitudes of the first two days, albeit the measurement of March 4
was acquired under bad weather conditions (thick cirrus), seem to confirm
the deviations of the decay of this object from the typical power-law
trend seen in GRB afterglows, as already pointed out by other authors (see
GCN #581 and #586).
The present data also agree with the result reported by Boer & Veillet
(GCN #598) and indicate a "standstill" of the optical candidate. Thus,
either we are already seeing the host galaxy of this GRB (in this case it
would not be the object at 1" W, 2" N of the transient; see GCN #592,
#594, #598), or the optical transient associated to GRB000301C has a
definitely peculiar behaviour, or this is not the optical counterpart of
GRB000301C.
We also obtained B and I images which are now entering the reduction
stage.
- GCN notice #600
James Rhoads and Andy Fruchter (STScI) report:
We observed the candidate counterpart of GRB 000301c again on March 8.590
in the K' filter using the NASA IRTF + NSFCam. The magnitude of the transient
relative to the reference star 6" west has decayed further to +3.32 +- 0.09,
giving K'=19.28 +- 0.09 (statistical error only).
This is a decay of 0.72 magnitudes in the two days since our preceding
observation (on March 6.595 UT).
This continued decay is in marked contrast to the "standstill" of the
optical flux reported by Bernabei et al (GCNC 599), and leads us to
believe that the source most likely is the transient counterpart of
GRB 000301c despite its erratic behavior. The near-IR flux showed a
comparable "standstill" behavior earlier (GCNC 572, 577, 586, 587) and then
entered a steeper decline. The total decay to date in K' has been 1.76
magnitudes, and during the 72 hours preceding this observation the K' flux
decayed approximately as t**(-2.2).
Extrapolation of this object's light curve from earlier data appears
fraught with difficulty. Further observation is therefore strongly
urged at all wavelengths.
- GCN notice #602
A. Fruchter (STScI), A. Smette (GSFC), T. Gull (GSFC), R. Gibbons,
H. Ferguson, L. Petro, K. Sahu (STScI) for a larger HST GRB Collaboration.
We have imaged the field of GRB 000301C with HST using the STIS CCD
50LP (open) mode. The observations were performed on the 6.22 March
2000 UT with a total exposure time of 1440s. We easily detect the
transient believed to be associated with GRB 000301C (Fynbo et al GCN
570, Bernabei et al. GCN 571). We find a source magnitude of
R=21.5 +/- 0.15 or V=21.9 +/- 0.15, where the error is dominated by
the wide bandpass of the STIS detector and the uncertainty in the color
of the transient (Halpern et al. GCN 585).
The OT is relatively well represented by a point source: any underlying
galaxy would have to have R >~ 24, or be unusually compact for it to
avoid detection in our data. We therefore believe that the apparent
flattening of the light curve in the R band reported by many observers
is not due to an underlying host galaxy but rather is intrinsic to
transient.
The red galaxy to the north east of the transient reported by Rhoads
and Fruchter (GCN 586) is detected in our image; however, there is no
apparent bridge of emission between these two objects. We therefore
now believe it is quite likely that they are unrelated.
The image is available at
http://www.stsci.edu/~fruchter/GRB/000301C
A portion of the HST/STIS CCD image of the field of GRB 000301C
(10" across). The transient is the star in the upper
left hand (north west) corner of the field. The galaxy previously
identified as a possible host is to its upper right. The lack of emission
between the two, and the good fit between the transient and the STIS PSF
suggests that the host galaxy of this transient has not yet been detected.
- GCN notice #603
A. Smette (NASA/GSFC,NOAO,FNRS), A. Fruchter (STScI), T. Gull (NASA/GSFC),
K. Sahu, H. Ferguson, L. Petro (STScI), and D. Lindler (ACC) report for
the HST GRB collaboration and the Danish discovery team:
The proposed optical counterpart of GRB 000301C (Fynbo et al GCN 570,
Bernabei et al. GCN 571) was observed with HST/STIS-PRISM mode during
four orbits totaling 8000s from 6.26 to 6.49 March 2000 (UT). The
MAMA NUV detector with sensitivity from 1175A to 3400A was used. Data
reductions were performed with STIS GTO IDL tools using prelaunch
spectral dispersion constants and on-orbit sensitivity calibrations.
A spectrum is detected with a peak S/N ~ 10 beginning at ~2650A,
extending to ~3250A with an average flux of ~4.6+/-0.2E-18 ergs/cm2/sec.
The emission is 2.2 pixels FWHM (0.055 arcseconds) along the slit
indicating a point source with no obvious diffuse extension. The
spectrum appears relatively flat (in f_lambda) from 3200A to 2750A and
then presents a sharp drop at about 2700A.
Within the present calibration uncertainties, the observed spectrum is
well fitted by a model using the power-law spectral index determined
by Halpern et al. (GCN 585), the observed V = 21.9 magnitude from the
STIS CCD images obtained on 6.2 March (Fruchter et al. GCN 602) a
moderate amount of extinction in the restframe of the OT, and a Lyman
limit break at ~2700A.
Assuming the Lyman break is caused by neutral hydrogen in the host
galaxy, the redshift of GRB 000301C is 1.95 +/- 0.1 where the large
error bar is due almost entirely to the present uncertainty in the
STIS UV prism calibration. We expect a more accurate calibration
shortly.
We encourage ground-based observations at a predicted Lyman alpha
wavelength of 3585+-120A. H alpha would be at ~1.95 microns.
- GCN notice #604
J. P. Halpern & J. Kemp (Columbia U.) report on behalf of
the MDM Observatory GRB follow-up team:
We reobserved GRB 000301C in the R band on March 9.52 UT using
the MDM 1.3m telescope, measuring R = 22.28 +/- 0.09 referenced
to the comparison stars of Garnavich et al. (GCN #573). Seeing
was 1."4. If we restrict our attention to those GCN reported
magnitudes that have error bars less than or equal to 0.1 mag,
then the light curve is reasonably well described by a power-law
decay of alpha = -0.90 +/- 0.04 until 4 days after the burst,
followed by a power-law decay of alpha = -1.93 +/- 0.12.
An updated decay curve and a new CCD image are posted at
http://www.astro.bio2.edu/grb/000301Ca
- GCN notice #605 >BR>
S. M. Castro, A. Diercks, S. G. Djorgovski, S. R. Kulkarni, T. J. Galama,
J. S. Bloom, F. A. Harrison (Caltech), and D. A. Frail (NRAO), report on
behalf of the Caltech-CARA-NRAO GRB collaboration:
Moderately high resolution spectra (FWHM ~ 1 Ang) of the optical transient
(OT) associted with GRB 000301C (Fynbo et al., GCN 570) were obtained on UT
2000 March 04, by W. L. W. Sargent, A. Boksenberg, and M. Rauch, using the
ESI Echelle spectrograph on the Keck-II 10-m telescope on Mauna Kea, Hawaii.
Two exposures of 1800 sec each were obtained, over an effective wavelength
range from ~3800 Ang, to ~10800 Ang. The OT continuum is well detected.
No strong absorption systems were found in the spectrum. However, a number
of possible weak lines are present. We identify a subset of them with the
following lines: Fe II 2260, 2344, 2374, 2382, 2586, and 2600, and Mg II 2796
and 2803; and a less reliable set of O I 1302, C II 1334, Si IV 1393,
Si II 1526, C IV 1550, Fe II 1608, Al II 1670. The weighted mean absorption
redshift of this 16-line system is z = 2.0335 +- 0.0003.
This is fully consistent with the redshift estimate from the HST spectroscopy,
z = 1.95 +- 0.1 (Smette et al., GCN 603), based on the ostensible Lyman break.
We thus consider our redshift determination to be secure, and interpret it as
the redshift of the GRB host galaxy, with no intervening foreground systems.
The restframe equivalent widths of the absorption lines are in the range of
interstellar medium in the host galaxy.
Assuming z = 2.0335, and a simple Friedmann cosmology with H_0 = 65 km/s/Mpc,
Omega_0 = 0.2, and Lambda_0 = 0, the luminosity distance is D_L = 5.11e28 cm,
the distance modulus is (m-M) = 49.1 mag, and the relativistic (1+z)**4
surface brightness dimming factor is 4.8 mag. This may account for the lack
of a detection of the host galaxy in the HST images (Fruchter et al., GCN 602).
- GCN notice # 606 and #607 >BR>
Feng, M., Wang, L., and Wheeler, J. C., University of Texas at Austin report:
We obtained a low resolution (resolving power about 500) spectrum of
GRB 000301c with the 2.7 meter telescope at McDonald Observatory on 2000
March 3.47. The total exposure time was 3900 seconds with wavelength
coverage from 318 nm to 589 nm. The low S/N (about 2-4) spectrum can be
fitted with a power law of spectral index beta = -1.1 witn no obvious
breaks after correcting for interstellar extinction assuming R = 3.1,
E(B-V) = 0.05 (cf GCN 585). The flux level is around 2.5E-17 ergs/cm2/sec/A.
This puts any possible Lyman break at wavelengths shorter than 318 nm.
The object is thus at a redshift lower than 2.5. This is consistent with
the report by Smette et al. (GCN 603).
The spectrum may reveal two absorption features at 336.0 nm and
352.2 nm. If identified with Lyman alpha, the redshifts of these features
are 1.76 and 1.89. The data also show another absorption feature at
367.1 nm, but with even lower confidence level. This feature yields
a redshift of 2.02 if identified with Lyman alpha. Another possible
feature is an absorption at 405.8 nm which might be identified with
C II 133.5 nm at a redshift of 2.04.
- GCN notice #610
The candidate for the optical transient (OT) associated with the gamma ray burst
GRB000301C has been observed in imaging mode with OSIS on the 3.6-m CFH
Telescope
in the course of the French GRB follow-up program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
The OT has the following magnitude, using star A (GCN 573) photometry
(GCN 583):
R = 23.02 +/- 0.10 2000 March 11.63 (UTC)
The power-law decay observed lately (after 4 days after the burst, as described
by Halpern et al. GCN604) can now be described with alpha = 2.1 +/- 0.1.
Note that alpha is dependent on the choice of the start of the "new decay" and
on the inclusion or not of some of the measurements from Bernabei et
al. (GCN 599).
In case you read the introduction too fast, the instrument used is no longer
MOS, but OSIS. The detector is the same though (STIS2).
The new image is available at
http://www.cfht.hawaii.edu/~veillet/grb.html .
M. Pakull is acknowledged for his help in this observation.
- APOD
The HST image of GRB 000301C is
Astronomy Picture of the Day 2000 March 14.
- GCN notice #611
The candidate for the optical transient (OT) associated with the gamma
ray burst GRB000301C has been observed in imaging mode with OSIS on
the 3.6-m CFH Telescope in the course of the French GRB follow-up
program at CFHT (M. Boer, CESR, C. Veillet, CFHT).
The OT has the following magnitude, using star A (GCN573) photometry
(GCN583):
R = 23.82 +/- 0.10 2000 March 14.60 (UTC)
(two 30mn exposures)
B = 24.83 +/- 0.12 2000 March 14.60 (UTC)
(one 55mn exposure)
The power-law decay described with alpha = -2.1 +/- 0.1 (GCN610) is not
sufficient to account properly for the last four measurements (GCN598,
604, 610 and this GCN), which are better fit with alpha = -2.7 +/- 0.1 .
The first phase of the decay would cover the first four days after the
burst, with alpha = -0.91 +/- 0.08. A graph with these two consecutive
power laws, as well at the new images, are at
http://www.cfht.hawaii.edu/~veillet/grb.html.
As for the apparent B-R, the error bars are large enough to make it close
to the value determined using MOS on March 3.5 (0.86 +/- 0.06) or the one
published by Halpern (0.77 +/- 0.06 in GCN 585 a week ago).
As the GRB is still steadily decaying, it's unlikely to have the underlying
galaxy contributing significantly to the measured flux. This galaxy should
probably be fainter than R = 24.5, confirming the comment by Fruchter et al.
(GCN602) from HST imaging data (R >~ 24).
A 20 micron camera will be installed on the telescope today for 10 nights.
No new data on this GRB will be acquired during this period.
I. Gable is acknowledged for his help in this observation.
- GCN notice #623
The candidate for the optical transient (OT) associated with the gamma
ray burst GRB000301C has been observed using the CFH12K CCD mosaic
camera at the prime focus of the 3.6-m CFH Telescope in the course of
the French GRB follow-up program at CFHT (M. Boer, CESR, C. Veillet,
CFHT).
Three 12 mn exposures with moderate seeing (image quality around 0.9") have
been coadded.
There is nothing visible at the location of the OT. The nearby galaxy
(thought to be the host for some time before the HST observations) has a
magnitude of R= 24.5 +-0.1, confirming the previous determinations (GCN592
- GCN598).
The faintest objects detected in the neighborhood are at around R=26.
We can infer the following lower limit:
R > 26.0 on 2000 April 4.6
It is compatible with the alpha = -2.7 power law decay given in GCN611, and
not with alpha = -2.1 given earlier, which would lead to R~25.6 at the
same epoch.
Further imaging is planned if the seeing gets better.
Jean-Charles Cuillandre is acknowledged for his help in this observation.
- GCN notice #624
A composite image of the GRB field without anything at the
location of the OT is posted at
http://www.cfht.hawaii.edu/~veillet/grb.html
An obvious consequence of the magnitude limit given in GCN623
is that the host galaxy is fainter than R=26 ...
I should have included that in the previous GCN. Sorry!
- GCN notice #627
A. Fruchter (STScI), A. Smette (GSFC), T. Gull (GSFC), H. Ferguson, L. Petro,
J. Rhoads, and K. Sahu (STScI) for a larger HST GRB Collaboration:
We have re-imaged the field of GRB 000301C with HST using the STIS CCD
in both 50CCD (open) and LP (long-pass) mode. The observations were
centered about 3.9 April 2000 UT with total exposure times of 2280s
in both filters.
We detect a bright source on a fainter extended object at the position
of the optical transient (OT). The position of the peak of emission
from the object agrees with that of the OT on previous HST images taken
on 6 March 2000 (see GCN 602) to better than 0."01, based on astrometry
relative to other objects visible in both HST images. We believe
therefore we are observing continued emission from the OT of GRB 000301c,
as well as from its host galaxy. One cannot give a precise magnitude
for the OT without knowing a priori the surface brightness profile of
the host. However, what we consider the best point source subtraction
implies an OT magnitude of R=26.9; in any case, the point source is
no brighter than R=26.7. The total magnitude of the OT plus
host is 26.5 +/- 0.15 on 3.9 April 2000. Although no upper limit
to the magnitude of the OT can truly be given without knowledge
of the host, we note that R=26.9 is within 0.1 mag of the value
predicted for this date by the fit to earlier R band data given
in Rhoads and Fruchter (astro-ph/0004057). This provides some further
confidence that our best estimate of the OT strength is not far off.
If this value is used for the magnitude of the OT, then the host galaxy
has a magnitude R = 27.8 +/- 0.25.
The STIS filter set only gives limited color information, however,
our observations agree well with the spectral index of -0.9
reported by Halperin (GCN 585). A change to a spectral index
of -3, as has been seen in the late time spectra of some other
GRBs, would most likely have been detected.
The HST images of GRB 000301c are available at:
http://www.stsci.edu/~fruchter/GRB/000301C
- GCN notice #630
SG Bhargavi and R Cowsik (IIA, Bangalore) report the
results of optical data on GRB000301c observed
between Mar 2-4, 2000 (GCN-591):
Mar 2.9618UT R=20.02 \pm 0.03, B-R=0.97 \pm 0.2
Mar 4.9087UT R=20.58 \pm 0.05, B-R=0.734 \pm 0.14
Mar 3.9976UT R=20.49 \pm 0.10
The R-band magnitudes from VBT along with other values
from various GCN circulars have been plotted. The numbers marked
on the graph correspond to the serial number of entries in the table.
Two solid lines are fit by alpha = -0.722 +/- 0.05 and
alpha=-2.9 +/- 0.017, which seems to be a better fit than the dotted
lines where the power law index is alpha = -0.97+/- 0.07 and
alpha= -1.99 +/- 0.19 respectively.
(Mid-expoure time for B-R is 2.975UT and 4.9375UT respectively;
this combined with B-R values in GCN \#588, 585 shows that B-R is
falling as -0.25mag/day)
The table as well as the graph (post-script file) are available
at our anonymous FTP server: narmada.iiap.ernet.in/bhargavi/GRB000301c/
- GCN notice #701
A. Fruchter, M. Metzger and L. Petro report for a larger collaboration:
The field of GRB 000301c was reobserved by the Hubble Space Telescope
using the STIS camera in open (50CCD) mode on the 19 April 2000. The
optical transient is still visible with an R magnitude of 27.9 +/-
0.15, where the error is dominated by uncertainties in the calibration
of STIS and the need to assume the shape of the spectrum across the
wide bandpass of the detector. The OT therefore is continuing the
steep decline reported in the previous GCN and remains consistent with
the late-time power-law reported in Rhoads and Fruchter
(astro-ph/0004057).
We find no evidence of a host galaxy underlying the GRB, to a magnitude
of at least 28.5. We believe the apparently extended emission
reported in our previous GCN is due to substantial, and larger than
expected, variability in the PSF. Although we have not yet been able
to fully reproduce the emission about the point source in our 3
April 2000 observations, we suspect this is due to very rapid variability
in the PSF. Further analysis of our data has now shown residuals in PSF
subtraction comparable in magnitude to that seen in the 3 April observation,
even when using PSFs from the same star taken in quick succession.
- GCN notice #766
K. Z. Stanek (CfA), P. Garnavich (Notre Dame), P. Barmby, S. Jha (CfA)
report:
Given the microlensing interpretation of GRB000301C (Garnavich, Loeb &
Stanek 2000b: astro-ph/0008049) and the importance of any additional
data for this burst, we reduced several additional frames of the
optical counterpart of GRB000301C obtained with the FLWO 1.2m
telescope and UBVI filters on 2000 Mar. 4 (UT).
Our measurements are based on the comparison star A of Garnavich et
al. (2000a: GCN 573), calibrated by Henden (2000: GCN 583) (magnitudes
given by Jensen et al. 2000: astro-ph/0005609). We obtain the
following values:
Mar. 4.5097 UT U=20.89 +- 0.13
Mar. 4.499 UT B=21.49 +- 0.05
Mar. 4.478 UT V=20.98 +- 0.05
Mar. 4.485 UT I=20.28 +- 0.07
As discussed by Garnavich et al. (2000b), to take full advantage of
this unique burst a uniform reduction of all CCD data available would
be most desired. To encourage such an endeavor, we make all our CCD
data (seven 1kx1k frames; see also GCN 573 and 581) publicly available
through the anonymous ftp at
ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB000301C/
Please contact K. Z. Stanek (kstanek@cfa.harvard.edu) if you have any
questions concerning the data.
- Lightcurve from the CfA-GRB group (astro-ph/0008049) suggesting
a microlensing event
- GCN notice #1063
A. Fruchter and P. Vreeswijk report for a larger collaboration:
The field of GRB 000301c was reobserved by the Hubble Space Telescope
using the STIS camera in open (50CCD) mode on the 25 Feb 2001, or
nearly one year after outburst. Twelve dithered exposures were
combined to produce a final image with an exposure time of 7031s.
No source is immediately visible at the position of the GRB. However,
when the image is convolved with gaussians or boxcars with
characteristic sizes from that of the PSF, 0."08, to 0."2, an extended
object appears to be visible under the position of the GRB and to its
NE. Although extended light from both a nearby bright star, and the
larger galaxy to the NW of the GRB make an exact determination of the
significance of this object difficult, we believe this is approximately
a 3-4 sigma detection. The probable host has an estimated magnitude of
R = 28.0 +/- 0.3. This magnitude is just consistent with the estimates
of an underlying host from our earlier imaging, GCN 627 and 701. It
is, furthermore, about two magnitudes brighter than we would expect the
OT to have been at this time, had it continued to decline with a
temporal power-law steeper than -2 (c.f. GCN 701 and Rhoads and
Fruchter, ApJ 2001, 546, 177).
If this is indeed a detection of a host, then in all cases where we
have obtained a deep HST image and an OT is well localized (to ~0."1),
a host has been found under the GRB. However, again, due to the
scattered and extended light in this region of the image, the detection
must be considered tentative.
The image can be seen at
http://www.stsci.edu/~fruchter/GRB/000301C
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