- GCN Circular #39660
K. Tatano, H. Negoro, M. Nakajima (Nihon U.), M. Serino, Y. Kawakubo (AGU),
Y. Kudo, H. Shibui, K. Takagi, H. Takahashi, H. Nishio (Nihon U.),
T. Mihara, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, Y. Kondo, S. Sasao, A. Yoshida (AGU),
Y. Tsuboi, H. Sugai, N. Nagashima (Chuo U.),
M. Shidatsu, Y. Niida (Ehime U.),
I. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech),
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA),
Y. Ueda, Y. Okada, K. Fujiwara (Kyoto U.),
M. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.),
K. Yamaoka (Nagoya U.),
M. Sugizaki (Kanazawa U.),
W. Iwakiri (Chiba U.),
T. Kawamuro (Osaka U.)
report on behalf of the MAXI team:
The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at
01:55:22 UT on March 11, 2025.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (224.318 deg, -2.613 deg) = (14 57 16, -02 36 46) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.33 deg and 0.28 deg, respectively.
The roll angle of long axis from the north direction is 9.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 75 +- 18 mCrab
(4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(223.607, -1.537) deg = (14 54 25, -01 32 13) (J2000)
(223.164, -1.982) deg = (14 52 39, -01 58 55) (J2000)
(225.099, -3.901) deg = (15 00 23, -03 54 03) (J2000)
(225.542, -3.455) deg = (15 02 10, -03 27 18) (J2000)
There was no significant excess flux in the previous transit at 00:22 UT
and in the next transit at 03:28 UT with an upper limit of 20 mCrab for each.
We note that the source position is consistent with the position of GRB 250305A
reported by Fermi-GBM (#39597). We encourage follow-up observations.
- GCN Circular #39664
X. Mao (NAO, CAS), Y. J. Zhang (THU), Y. L. Hua (PMO, CAS), Z. X. Ling (NAO, CAS) report on behalf of the Einstein Probe team:
We report on the detection of a fast X-ray transient EP250311a at 2025-03-11T01:56:19 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The position of the source is R.A. = 224.691 deg, DEC = -2.850 deg (J2000) with an uncertainty of 2.8 arcmin (radius, 90% C.L. statistical and systematic). EP250311a may be associated with GRB 250311A/MAXI J1457-026 reported by the MAXI team (GCN #39660) due to their temporal and spatial coincidence.
The transient event lasted for about 150 seconds, with a peak flux of about 1.6 x 10^-9 erg/s/cm^2 in 0.5-4 keV. The average spectrum during the burst can be fitted with an absorbed powerlaw model, with nH fixed at the Galactic value of 6.4 x 10^20 cm^-2 and a photon index of 1.4 (-0.8/+0.8). The unabsorbed average 0.5-4 keV flux is estimated to be 6.1 (-1.9/+3.1) x 10^-10 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters.
The FXT follow-up observations have been scheduled. Further follow-up observations are encouraged to identify the nature of this X-ray transient.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
- GCN Circular #39665
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a series of observations, tiled on the sky, of the
MAXI GRB 250311A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00135
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the MAXI event is high: any X-ray source
considered to be a probable afterglow candidate will be reported via a GCN Circular
after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
- GCN Circular #39667
W.X. Li (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), N.C. Sun, D. Xu, Z. Fan, Y.N. Wang (NAOC), report on behalf of a large collaboration:
We observed the field of GRB 250311A/EP250311a detected by MAXI (Tatano et al. GCN 39660) and EP (Mao et al., GCN 39664), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Sierra Remote Observatories in California. Observations started at 12:00:05 UT on 2025-03-11, i.e., ~10 hours after the EP trigger, and 2 x 300s frames were obtained in the R band.
No uncatalogued optical source is detected in the stacked R-band image within the EP/WXT error circle, down to the 3-sigma limiting magnitude of R ~ 20.
- GCN Circular #39677
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin,
V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the EP250311a ( EP Team et al., GCN 39664) errorbox 37833 sec after notice time and 68809 sec after trigger time at 2025-03-11 21:03:08 UT, with upper limit up to 17.4 mag. The observations began at zenith distance = 79 deg. The sun altitude is -46.6 deg.
The galactic latitude b = 47 deg., longitude l = 354 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2808566
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
68839 | 2025-03-11 21:03:08 | MASTER-SAAO | (14h 55m 03.37s , -02d 44m 11.8s) | C | 60 | 17.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
- GCN Circular #39681
J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P.
Beardmore (U. Leicester), J.P. Osborne (U. Leicester), R. Brivio
(INAF-OAB), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR) and P.A.
Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 250311A/MAXI J1457-026 (GCN Circ. 39660) in a series of
observations tiled on the sky. The total exposure time is 1.4 ks,
distributed over 4 tiles; the maximum exposure at a single sky location
in the tiling was 731 s. The data were collected between T0+34.4 ks and
T0+36.0 ks, and are entirely in Photon Counting (PC) mode.
Two uncatalogued X-ray sources have been detected, however none of them
is above the RASS limit or shows definitive signs of fading. Therefore,
at the present time we cannot identify which, if any, is the afterglow.
Details of these sources are given below:
Source 1:
RA (J2000.0): 224.4476 = 14:57:47.43
Dec (J2000.0): -2.7859 = -02:47:09.2
Error: 9.8 arcsec (radius, 90% conf.)
Count-rate: (9.8 [+6.3, -4.5])e-3 ct s^-1
Distance: 777 arcsec from MAXI position.
Source 2:
RA (J2000.0): 224.4381 = 14:57:45.15
Dec (J2000.0): -2.7813 = -02:46:52.7
Error: 8.7 arcsec (radius, 90% conf.)
Count-rate: 0.0134 [+0.0074, -0.0055] ct s^-1
Distance: 744 arcsec from MAXI position.
We note that these observations do not cover the localisation of X-ray
transient EP250311a (GCN 39664), which may be associated with the same
trigger.
The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00135.
This circular is an official product of the Swift-XRT team.
- GCN Circular #39683
A. Sankar. K, M.-H. Lee, A. Aryan, Y.-H. Lee, C.-H. Lai, T.-W. Chen, H.-Y. Hsiao, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, C.-S. Lin, Y.-C. Pan, C.-C. Ngeow, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
We observed the field of the fast X-ray transient GRB 250311A/EP250311a (Tatano et al., GCN 39660; Mao et al., GCN 39664) using the 40cm SLT and 1 meter LOT telescopes at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first SLT epoch of observations in the r band started at 15:28 UT on the 11th of March 2025 (MJD = 60745.6442), ~13.52 hrs after the EP trigger, while the first LOT epoch of observations in the r band started at 17:01 UT on the 11th of March 2025 (MJD = 60745.7090), ~ 15.08 hrs after the EP trigger.
We utilised the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. We did not detect any uncataloged optical counterpart candidate within the EP-WXT localization error circle of radius 2.8 arcminutes in the stacked image.
Moreover, we employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction utilizing the "sfft" (Hu, 2022, ApJ, 936, 157) algorithm using a template from SkyMapper DR4 (Onken et., 2024, PASA, 41, e061). We found no evidence of any prominent candidate optical counterpart in the difference image as well.
We further employed the Python-based package AutoPhOT to perform PSF photometry on our stacked frames. The details of the observations and measured 3-sigma upper limits (in the AB system) were as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
SLT | r | 60745.6442 | 13.52 | 300 * 9 | >19.6 | 1".5 | 2.04
LOT | r | 60745.7090 | 15.08 | 300 * 6 | >21.2 | 1".3 | 1.36
The non-detection of any prominent optical counterpart is consistent with Li et al. (GCN 39667).
The presented upper limits were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.27 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011).
- GCN Circular #39700
X. Mao (NAO, CAS), Y. J. Zhang (THU), Y. L. Hua (PMO, CAS), Z. X. Ling (NAO, CAS) report on behalf of the Einstein Probe team:
Following the detection of the fast X-ray transient EP250311a (Mao et al., GCN 39664), also detected as GRB 250311A by MAXI (Tatano et al., GCN 39660), we performed an observation with the Follow-up X-ray Telescope (FXT) on board Einstein Probe. The observation began at 2025-03-12T15:29:21 (UTC), about 38 hours after the EP-WXT detection, with an exposure time of 6048 seconds. Two uncatalogued sources were detected within the WXT error circle, at R.A., DEC = 224.7009, -2.8412 deg (J2000) and R.A., DEC = 224.7199, -2.8760 deg (J2000), respectively, with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). Both of the sources have the flux at the level of ~ 5e-14 erg/cm2/s in 0.5-10 keV. No previously known X-ray sources are found within the FXT error circle around the two sources.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
- GCN Circular #39718
X. Mao (NAO, CAS), Y. J. Zhang (THU), Y. L. Hua (PMO, CAS), Z. X. Ling (NAO, CAS) report on behalf of the Einstein Probe team:
The detection time for the transient EP250311a/GRB 250311A reported in GCN 39664 is incorrect: the corrected EP-WXT detection time is 2025-03-11T01:55:13 (UTC). We apologize for the mistake and any inconvenience caused by this, and thank MAXI team for their suggestion of a reanalysis on the data.
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