Gamma-ray Burst 220306B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 06 Mar 22 18:15:57 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1095288,   Seg_Num: 0
GRB_RA:            5.378d {+00h 21m 31s} (J2000),
                   5.698d {+00h 22m 47s} (current),
                   4.666d {+00h 18m 40s} (1950)
GRB_DEC:         +71.354d {+71d 21' 14"} (J2000),
                 +71.477d {+71d 28' 36"} (current),
                 +71.076d {+71d 04' 35"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       1502 [cnts]    Image_Peak=179 [image_cnts]
TRIGGER_DUR:     0.512 [sec] 
TRIGGER_INDEX:   124     E_range: 25-100 keV
BKG_INTEN:       12913 [cnts]
BKG_TIME:        65723.26 SOD {18:15:23.26} UT
BKG_DUR:         8 [sec]
GRB_DATE:        19644 TJD;    65 DOY;   22/03/06
GRB_TIME:        65737.47 SOD {18:15:37.47} UT
GRB_PHI:         124.85 [deg]
GRB_THETA:        18.27 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     22.78 [sigma]
IMAGE_SIGNIF:    12.05 [sigma]
MERIT_PARAMS:     +1  +0  +0  -1  +2  +1  +0  +1 -21  +0 
SUN_POSTN:       347.26d {+23h 09m 02s}   -5.46d {-05d 27' 39"}
SUN_DIST:         77.89 [deg]   Sun_angle= -1.2 [hr] (East of Sun)
MOON_POSTN:       33.70d {+02h 14m 49s}  +11.79d {+11d 47' 07"}
MOON_DIST:        62.08 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:      120.52,  8.62 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       51.79, 59.03 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 274.94,14.13 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 06 Mar 22 18:17:09 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1095288,   Seg_Num: 0
POINT_RA:          5.346d {+00h 21m 23s} (J2000)
POINT_DEC:       +71.347d {+71d 20' 50"} (J2000)
IMG_START_DATE:  19644 TJD;    65 DOY;   22/03/06
IMG_START_TIME:  65823.39 SOD {18:17:03.39} UT,   85.9 [sec] since BAT Trigger Time
COUNTS:          39    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        4    Max_iter_allowed= 4
ERROR_CODE:      2
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        Algorithm did not converge; too many iterations.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 06 Mar 22 18:20:04 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1095288,   Seg_Num: 0
GRB_RA:            5.378d {+00h 21m 31s} (J2000),
                   5.698d {+00h 22m 47s} (current),
                   4.666d {+00h 18m 40s} (1950)
GRB_DEC:         +71.354d {+71d 21' 14"} (J2000),
                 +71.477d {+71d 28' 36"} (current),
                 +71.076d {+71d 04' 35"} (1950)
GRB_DATE:        19644 TJD;    65 DOY;   22/03/06
GRB_TIME:        65737.47 SOD {18:15:37.47} UT
TRIGGER_INDEX:   124
GRB_PHI:         124.85 [deg]
GRB_THETA:        18.27 [deg]
DELTA_TIME:      19.00 [sec]
TRIGGER_DUR:     0.512 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     22.78 [sigma]
IMAGE_SIGNIF:    12.05 [sigma]
LC_URL:          sw01095288000msb.lc
SUN_POSTN:       347.26d {+23h 09m 02s}   -5.46d {-05d 27' 35"}
SUN_DIST:         77.89 [deg]   Sun_angle= -1.2 [hr] (East of Sun)
MOON_POSTN:       33.74d {+02h 14m 57s}  +11.80d {+11d 47' 60"}
MOON_DIST:        62.07 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:      120.52,  8.62 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       51.79, 59.03 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 274.94,14.13 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 06 Mar 22 18:21:00 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1095288,   Seg_Num: 0
POINT_RA:          5.346d {+00h 21m 23s} (J2000)
POINT_DEC:       +71.347d {+71d 20' 50"} (J2000)
POINT_ROLL:      198.430d
IMG_START_DATE:  19644 TJD;    65 DOY;   22/03/06
IMG_START_TIME:  65826.52 SOD {18:17:06.52} UT,   89.1 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.702
N_STARS:         125
X_OFFSET:        379 [pixels]
Y_OFFSET:        537 [pixels]
X_MAX:           1338 [pixels]
Y_MAX:           1496 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    10
SL_URL:          sw01095288000msufc0089.fits
SUN_POSTN:       347.26d {+23h 09m 03s}   -5.46d {-05d 27' 34"}
SUN_DIST:         77.88 [deg]   Sun_angle= -1.2 [hr] (East of Sun)
MOON_POSTN:       33.74d {+02h 14m 58s}  +11.80d {+11d 48' 11"}
MOON_DIST:        62.07 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:      120.51,  8.62 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       51.77, 59.03 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 06 Mar 22 18:21:19 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1095288,   Seg_Num: 0
GRB_RA:            5.3870d {+00h 21m 32.87s} (J2000),
                   5.7067d {+00h 22m 49.60s} (current),
                   4.6747d {+00h 18m 41.92s} (1950)
GRB_DEC:         +71.3632d {+71d 21' 47.5"} (J2000),
                 +71.4861d {+71d 29' 09.9"} (current),
                 +71.0859d {+71d 05' 09.1"} (1950)
GRB_ERROR:       4.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  19644 TJD;    65 DOY;   22/03/06
IMG_START_TIME:  65848.00 SOD {18:17:28.00} UT,   110.5 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       347.26d {+23h 09m 03s}   -5.46d {-05d 27' 34"}
SUN_DIST:         77.90 [deg]   Sun_angle= -1.2 [hr] (East of Sun)
MOON_POSTN:       33.75d {+02h 14m 59s}  +11.80d {+11d 48' 15"}
MOON_DIST:        62.07 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:      120.52,  8.63 [deg] galactic lon,lat of the burst
ECL_COORDS:       51.81, 59.03 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 06 Mar 22 18:22:28 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1095288,   Seg_Num: 0
POINT_RA:          5.346d {+00h 21m 23s} (J2000)
POINT_DEC:       +71.347d {+71d 20' 50"} (J2000)
ROLL:            198.430d
IMG_START_DATE:  19644 TJD;    65 DOY;   22/03/06
IMG_START_TIME:  65826.52 SOD {18:17:06.52} UT,   89.1 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     668283455
X_OFFSET:        698 [pixels]
Y_OFFSET:        856 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       858
Y_GRB_POS:       1016
BINNING_INDEX:   1
IM_URL:          sw01095288000msuni0118.fits
SUN_POSTN:       347.26d {+23h 09m 03s}   -5.46d {-05d 27' 32"}
SUN_DIST:         77.88 [deg]   Sun_angle= -1.2 [hr] (East of Sun)
MOON_POSTN:       33.76d {+02h 15m 01s}  +11.81d {+11d 48' 30"}
MOON_DIST:        62.07 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:      120.51,  8.62 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       51.77, 59.03 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 06 Mar 22 18:22:42 UT
NOTICE_TYPE:     Swift-XRT Lightcurve
TRIGGER_NUM:     1095288,   Seg_Num: 0
POINT_RA:          5.342d {+00h 21m 22s} (J2000)
POINT_DEC:       +71.347d {+71d 20' 48"} (J2000)
LC_START_DATE:   19644 TJD;    65 DOY;   22/03/06
LC_START_TIME:   65826.07 SOD {18:17:06.07} UT,   88.6 [sec] since BAT Trigger Time
LC_STOP_DATE:    19644 TJD;    65 DOY;   22/03/06
LC_STOP_TIME:    66049.52 SOD {18:20:49.52} UT
LC_LIVE_TIME:    221.10 [sec], 98.9%
DELTA_TIME:      86176.55 [sec]
N_BINS:          100
TERM_COND:       0
LC_URL:          sw01095288000msx.lc
SUN_POSTN:       347.26d {+23h 09m 03s}   -5.46d {-05d 27' 32"}
SUN_DIST:         77.88 [deg]   Sun_angle= -1.2 [hr] (East of Sun)
MOON_POSTN:       33.76d {+02h 15m 02s}  +11.81d {+11d 48' 33"}
MOON_DIST:        62.07 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:      120.51,  8.62 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       51.77, 59.03 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-XRT Lightcurve.

GCN Circular #31697
R. Caputo (GSFC), A. P. Beardmore (U Leicester), C. Gronwall (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU), A. Y. Lien (U Tampa), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), T. M. Parsotan (GSFC/UMBC/CRESSTII), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team:
At 18:15:37 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 220306B (trigger=1095288). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 5.378, +71.354 which is
```
   RA(J2000) = 00h 21m 31s
   Dec(J2000) = +71d 21' 14"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 15 sec. The peak count rate was ~2600 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 18:17:03.3 UT, 85.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 5.38628, 71.36313 which is equivalent to:
```
  RA(J2000)  = 00h 21m 32.71s
  Dec(J2000) = +71d 21' 47.3"
```
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This location is 34 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 4.07 x 10^21 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 89 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.578.
Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)
GCN Circular #31702
J. Wood (NASA/MSFC) reports on behalf of the Fermi GBM Team:
"At 18:15:36.24 UT on 06 March 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 220306B (trigger 668283341 / 220306761) which was also detected by the Swift/BAT and Swift/XRT (Caputo et al. 2022, GCN 31697). The GBM on-ground location is consistent with the Swift position.
The GBM light curve consists of a single pulse with a duration (T90) of about 10.2 s (50-300 keV). The time-averaged spectrum from T0-1.0 s to T0+9.2 s is best fit by a Band function with Epeak = 160 +/- 122 keV, alpha = -1.1 +/- 0.3, and beta = -1.8 +/- 0.2
The event fluence (10-1000 keV) in this time interval is (1.7 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.2 s in the 10-1000 keV band is 2.8 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular #31703
A. D'Ai (INAF-IASFPA), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB) and R. Caputo report on behalf of the Swift-XRT team:
We have analysed 6.6 ks of XRT data for GRB 220306B (Caputo et al. GCN Circ. 31697), from 111 s to 24.3 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 31700).
The light curve can be modelled with a power-law decay with a decay index of alpha=0.88 (+0.17, -0.12).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+0.32, -0.29). The best-fitting absorption column is 7.1 (+2.9, -2.3) x 10^21 cm^-2, in excess of the Galactic value of 4.1 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.9 x 10^-11 (7.6 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:        7.1 (+2.9, -2.3) x 10^21 cm^-2
Galactic foreground: 4.1 x 10^21 cm^-2
Excess significance: 2.2 sigma
Photon index:        1.80 (+0.32, -0.29)
```
If the light curve continues to decay with a power-law decay index of 0.88, the count rate at T+24 hours will be 2.3 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-13 (1.7 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01095288.
This circular is an official product of the Swift-XRT team.
GCN Circular #31704
Y.-D. Hu, E. Fernandez-Garcia, T.-R. Sun, A. J. Castro-Tirado (IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco, A. Reina (Univ. de Malaga) and F. Rendon (IAA-CSIC and INTA-CEDEA) on behalf of a larger collaboration, report:
Following the detection of GRB 220306B by Swift (Caputo et al., GCNC 31697) and Fermi (Wood et al., GCNC 31702), the 0.3m BOOTES-1B robotic telescope in Mazagon (Huelva), southern Spain, automatically responded to this burst on Mar 7 at 00:05 UT (~5.8 hours after trigger). In the co-added frame (20 x 60 s, clear filter), no source is detected within the enhanced XRT position (Evans et al., GCNC 31700) down to 18.5 mag, which is consistent with the non-detections reported by UVOT (Caputo et al., GCNC 31697) and MASTER (Lipunov et al., GCNC 31699).
We thank the staff at INTA-CEDEA for their excellent support.
GCN Circular #31705
S. Belkin (IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO), N. Pankov (HSE, IKI), D. Datashvili (AbAO), V. R. Ayvazian (AbAO), G. V. Kapanadze (AbAO) report on behalf of GRB IKI FuN:
We observed� the field of Swift GRB 220306B (Caputo et al. GCN 31697) which is also detected by GBM/Fermi (Wood et al., GCN 31702) with AS-32 telescope of Abastumani observatory (AbAO) in R-filter starting on Mar. 06 (UT) 18:32:11. We detected the object at the edge (2.6 arcsec apart) of the enhanced XRT position (Evans et al. GCN 31700). The object is also presented in Pan-STARRS as a red source (objID 193630053894966412, r=21.42, i= 20.70, z=20.54). Due to non-optimal seeing we cannot discriminate a possible optical afterglow from the object. Preliminary aperture photometry of the object is following
```
Date������ UT start�� t-T0��� Filter Exp.��� OT��  Err.� UL(3sigma)
    �������������������(mid, days)��� (s)

2022-03-06 18:32:11��  0.02886� R���� 50*60��19.98 0.12 �� 22.7
```
The R magnitude of the object seems to be brighter than R_mag deduced for the object assuming the object is a star. We may suggest the afterglow superimposed of the object (Pan-STARRS objID 193630053894966412) and the red PanSTARRS object could be a host galaxy of GRB 220306B.
GCN Circular #31707
S. D. Barthelmy (GSFC), R. Caputo (GSFC) H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC), T. Sakamoto (AGU), M. Stamatikos (OSU) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 220306B (trigger #1095288) (Caputo et al., GCN Circ. 31697). The BAT ground-calculated position is RA, Dec = 5.380, 71.384 deg which is
```
   RA(J2000)  =  00h 21m 31.3s
   Dec(J2000) = +71d 23' 04.1"
```
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 78%.
The mask-weighted light curve shows a single-peaked structure that starts at ~T-2 s, peaks at ~T0, and ends at ~T+12 s. T90 (15-350 keV) is 12.34 +- 3.24 sec (estimated error including systematics).
The time-averaged spectrum from T-1.82 to T+11.66 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.30 +- 0.20. The fluence in the 15-150 keV band is 6.0 +- 0.7 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.05 sec in the 15-150 keV band is 2.3 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/1095288/BA/
GCN Circular #31711
S. Klose, A. Nicuesa Guelbenzu, B. Stecklum, S. Melnikov, F. Ludwig (all TLS Tautenburg) report:
We observed the field of the Swift/Fermi GRB 220306B (Caputo et al., GCN 31697; Wood et al., GCN 31782) with the Tautenburg 1.34m Schmidt telescope equipped with the TAUKAM 6kx6k CCD camera. Observations were performed on March 8, 2022, between 00:03 and 00:34 UT, about 30 hours after the burst.
Inside the enhanced XRT error circle (Evans et al., GCN 31700) we do not detect any source. Close to the error circle we detect two sources.
Source 1 lies at RA, DEC (J2000) = 00:21:33.42, +71:21:46.7 (+/- 0.5 arcsec) and is located at the south-eastern border of the XRT error circle. For this source we measure the following AB magnitudes:
```
r = 21.33 +/- 0.16,
i = 20.67 +/- 0.10,
z = 20.28 +/- 0.16,
```
calibrated against the Pan-STARRS catalog.
This source was already detected and discussed by Belkin et al. (GCN 31705). Our r-band data confirm that it is fading and that light from an underlying permanent object starts to dominate.
Source 2 lies at at RA, DEC (J2000) = 00:21:33.52, +71:21:51.9 and is located at the north-eastern border of the enhanced XRT error circle. For this source we measure r > 22.2 (3 sigma), i = 21.27 +/- 0.17, z = 20.83 +/- 0.25. The nature of this source is uncertain; obviously it is unrelated to the GRB.
GCN Circular #31714
S. Belkin (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO), N. Pankov (HSE) report on behalf of GRB IKI FuN:
We observed the field of Swift GRB 220306B (Caputo et al. GCN 31697) which is also detected by GBM/Fermi (Wood et al., GCN 31702) with AZT-33IK telescope of Mondy observatory in R-filter starting on Mar. 07 (UT) 16:42:31. We detected the object (Belkin et al., GCN 31705; Klose et al., GCN 31711) at the S-E edge of the enhanced XRT position (Evans et al. GCN 31700). Due to non-optimal seeing we cannot discriminate a possible optical afterglow from the object. Preliminary aperture photometry of the object is following
```
Date       UT start   t-T0    Filter Exp.    OT    Err.  UL(3sigma)
                        (mid, days)    (s)

2022-03-07 16:42:31   0.94924  R     20*120  21.20 0.22    22.0
```
The R magnitude of the object seems still to be brighter than R_mag deduced for the object assuming the object is a star. Taking into account results of observations (Belkin et al., GCN 31705; this GCN) and Tautenburg observations (Klose et al., GCN 31711) we would more firmly suggest the object is the afterglow of GRB 220306B. The object Pan-STARRS objID 193630053894966412 could be a host galaxy of GRB 220306B.
GCN Circular #31737
S.Y. Fu, X. Liu, S.Q. Jiang, D. Xu (NAOC), Z.P. Zhu (NAOC, HUST), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:
We observed the field of Swift GRB 220306B (Caputo et al., GCN 31697) using the NEXT-0.6m telescope located at Nanshan, Xinjiang, China. We obtained 3x40 s and 1x60 s frames in the Sloan r-band, starting at 18:23:35 UT on 2022-03-06, i.e., 478 s after the BAT trigger.
No optical source is detected at the Enhanced Swift/XRT position (Evans et al., GCN 31700) in our stacked image, down to a limiting magnitude of r~19.3, calibrated with the nearby PanSTARRS field.
GCN Circular #31759
M. H. Siegel (PSU) and Caputo (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 220306B 89 s after the BAT trigger (Caputo et al., GCN Circ. 31697). No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 31700) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            89          239          147         >19.9
u_FC               302          552          246         >20.1
white               89         1716          402         >20.4
v                  631         1601          117         >18.7
b                  557         1701          117         >19.9
u                  302         1676          343         >20.2
w1                 680         1650          117         >19.3
m2                 656         1626          117         >19.4
w2                 607         5204          213         >19.4
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.578 in the direction of the burst (Schlegel et al. 1998).

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Jochen Greiner, last update: 07-Mar-2022 [Disclaimer]