Gamma-ray Burst 250321A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN/BACODINE POSITION NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Fri 21 Mar 25 00:43:00 UT
  NOTICE_TYPE:     Swift-BAT GRB Position
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  GRB_RA:          295.077d {+19h 40m 19s} (J2000),
                   295.351d {+19h 41m 24s} (current),
                   294.534d {+19h 38m 08s} (1950)
  GRB_DEC:         +21.041d {+21d 02' 27"} (J2000),
                   +21.101d {+21d 06' 03"} (current),
                   +20.924d {+20d 55' 27"} (1950)
  GRB_ERROR:       3.00 [arcmin radius, statistical only]
  GRB_INTEN:       3021 [cnts]    Image_Peak=183 [image_cnts]
  TRIGGER_DUR:     1.024 [sec] 
  TRIGGER_INDEX:   149     E_range: 25-100 keV
  BKG_INTEN:       15975 [cnts]
  BKG_TIME:        2540.71 SOD {00:42:20.71} UT
  BKG_DUR:         8 [sec]
  GRB_DATE:        20755 TJD;    80 DOY;   25/03/21
  GRB_TIME:        2558.89 SOD {00:42:38.89} UT
  GRB_PHI:          21.93 [deg]
  GRB_THETA:        44.31 [deg]
  SOLN_STATUS:     0x20000003
  RATE_SIGNIF:     21.97 [sigma]
  IMAGE_SIGNIF:    10.33 [sigma]
  MERIT_PARAMS:     +1  +0  +0  +0  +2  +0  +0  +1 -38  +0 
  SUN_POSTN:         0.60d {+00h 02m 25s}   +0.26d {+00d 15' 42"}
  SUN_DIST:         66.91 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
  MOON_POSTN:      252.04d {+16h 48m 10s}  -27.65d {-27d 39' 10"}
  MOON_DIST:        64.26 [deg]
  MOON_ILLUM:      64 [%]
  GAL_COORDS:       57.11, -0.69 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      302.01, 41.73 [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 = 169.98,7.43 [deg].  
  COMMENTS:           
  COMMENTS:        NOTE: This BAT event is temporally(1.0<100sec) coincident with the FERMI_GBM event (trignum=764210564).  
  

• red DSS finding chart ps-file
  
  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Fri 21 Mar 25 00:44:56 UT
  NOTICE_TYPE:     Swift-XRT Nack-Position
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  POINT_RA:        295.063d {+19h 40m 15s} (J2000)
  POINT_DEC:       +21.044d {+21d 02' 38"} (J2000)
  IMG_START_DATE:  20755 TJD;    80 DOY;   25/03/21
  IMG_START_TIME:  2683.59 SOD {00:44:43.59} UT,   124.7 [sec] since BAT Trigger Time
  COUNTS:          15    Min_needed= 20
  STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
  PH2_ITER:        2    Max_iter_allowed= 4
  ERROR_CODE:      1
  COMMENTS:        SWIFT-XRT Nack Position.  
  COMMENTS:        No source found in the image.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Fri 21 Mar 25 00:48:00 UT
  NOTICE_TYPE:     Swift-BAT GRB Lightcurve
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  GRB_RA:          295.077d {+19h 40m 19s} (J2000),
                   295.351d {+19h 41m 24s} (current),
                   294.534d {+19h 38m 08s} (1950)
  GRB_DEC:         +21.041d {+21d 02' 27"} (J2000),
                   +21.101d {+21d 06' 03"} (current),
                   +20.924d {+20d 55' 27"} (1950)
  GRB_DATE:        20755 TJD;    80 DOY;   25/03/21
  GRB_TIME:        2558.89 SOD {00:42:38.89} UT
  TRIGGER_INDEX:   149
  GRB_PHI:          21.93 [deg]
  GRB_THETA:        44.31 [deg]
  DELTA_TIME:      0.00 [sec]
  TRIGGER_DUR:     1.024 [sec] 
  SOLN_STATUS:     0x3
  RATE_SIGNIF:     21.97 [sigma]
  IMAGE_SIGNIF:    10.33 [sigma]
  LC_URL:          sw01297508000msb.lc
  SUN_POSTN:         0.61d {+00h 02m 26s}   +0.26d {+00d 15' 47"}
  SUN_DIST:         66.91 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
  MOON_POSTN:      252.09d {+16h 48m 21s}  -27.66d {-27d 39' 31"}
  MOON_DIST:        64.24 [deg]
  MOON_ILLUM:      64 [%]
  GAL_COORDS:       57.11, -0.69 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      302.01, 41.73 [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 = 169.98,7.43 [deg].  
  COMMENTS:        The 3rd packet (of 3) was missing in the lightcurve data stream.  
  

  
• GCN Circular #39793
  The Fermi GBM team reports the detection of a likely LONG GRB
  At 00:42:39 UT on 21 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250321A (trigger 764210564.016716 / 250321030).
  The on-ground calculated location, using the Fermi GBM trigger data, is RA = 299.0, Dec = 17.1 (J2000 degrees, equivalent to J2000 19h 56m, 17d 06'), with a statistical uncertainty of 6.3 degrees.
  The angle from the Fermi LAT boresight is 44.0 degrees.
  The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/quicklook/glg_skymap_all_bn250321030.png
  The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/quicklook/glg_healpix_all_bn250321030.fit
  The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/quicklook/glg_lc_medres34_bn250321030.gif
  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Fri 21 Mar 25 01:04:26 UT
  NOTICE_TYPE:     Swift-UVOT Source List
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  POINT_RA:        295.063d {+19h 40m 15s} (J2000)
  POINT_DEC:       +21.044d {+21d 02' 38"} (J2000)
  POINT_ROLL:      99.011d
  IMG_START_DATE:  20755 TJD;    80 DOY;   25/03/21
  IMG_START_TIME:  2686.79 SOD {00:44:46.79} UT,   127.9 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        7.683
  N_STARS:         113
  X_OFFSET:        565 [pixels]
  Y_OFFSET:        521 [pixels]
  X_MAX:           1524 [pixels]
  Y_MAX:           1480 [pixels]
  DET_THRESH:      24
  PHOTO_THRESH:    15
  SL_URL:          sw01297508000msufc0127.fits
  SUN_POSTN:         0.62d {+00h 02m 28s}   +0.27d {+00d 16' 03"}
  SUN_DIST:         66.93 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
  MOON_POSTN:      252.24d {+16h 48m 58s}  -27.68d {-27d 40' 42"}
  MOON_DIST:        64.15 [deg]
  MOON_ILLUM:      64 [%]
  GAL_COORDS:       57.11, -0.68 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      302.00, 41.74 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Source List.  
  

• GCN Circular #39794
  R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
  At 00:42:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250321A (trigger=1297508). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 295.077, +21.041 which is

     RA(J2000) = 19h 40m 19s
     Dec(J2000) = +21d 02' 27"
  

  with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Only the first 8 seconds of the BAT light curve after the trigger is available due to a telemetry gap. This data shows a complex structure with a duration of at least 10 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger.
  The XRT began observing the field at 00:44:43.60 UT, 125.6 seconds after the BAT trigger. No source was detected in the 2.5-s promptly available image. We are waiting for the full dataset to detect and localise the XRT counterpart.
  Due to a telemetry gap, UVOT data are not available at this time.
  Although XRT did not report an X-ray counterpart in the limited immediately transmitted data, the significance of the BAT image (>10 sigma), the shape of the BAT light curve, and the simultaneous detection by Fermi/GBM (trigger 764210564) give us confidence that this is an astrophysical Gamma Ray Burst.
  Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com). 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 NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Fri 21 Mar 25 01:04:42 UT
  NOTICE_TYPE:     Swift-UVOT Processed Source List
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  POINT_RA:        295.063d {+19h 40m 15s} (J2000)
  POINT_DEC:       +21.044d {+21d 02' 38"} (J2000)
  POINT_ROLL:      99.011d
  IMG_START_DATE:  20755 TJD;    80 DOY;   25/03/21
  IMG_START_TIME:  2686.79 SOD {00:44:46.79} UT,   127.9 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        7.683
  N_STARS:         113
  X_OFFSET:        565 [pixels]
  Y_OFFSET:        521 [pixels]
  X_MAX:           1524 [pixels]
  Y_MAX:           1480 [pixels]
  DET_THRESH:      24
  PHOTO_THRESH:    15
  SL_URL:          sw01297508000msufc0127.fits
  SUN_POSTN:         0.62d {+00h 02m 28s}   +0.27d {+00d 16' 04"}
  SUN_DIST:         66.93 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
  MOON_POSTN:      252.25d {+16h 48m 59s}  -27.68d {-27d 40' 43"}
  MOON_DIST:        64.15 [deg]
  MOON_ILLUM:      64 [%]
  GAL_COORDS:       57.11, -0.68 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      302.00, 41.74 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Processed Source List.  
  COMMENTS:        All 4 attachments are included.  
  

  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Fri 21 Mar 25 01:05:26 UT
  NOTICE_TYPE:     Swift-UVOT Processed Image
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  POINT_RA:        295.063d {+19h 40m 15s} (J2000)
  POINT_DEC:       +21.044d {+21d 02' 38"} (J2000)
  ROLL:            99.011d
  IMG_START_DATE:  20755 TJD;    80 DOY;   25/03/21
  IMG_START_TIME:  2686.79 SOD {00:44:46.79} UT,   127.9 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     764210722
  X_OFFSET:        884 [pixels]
  Y_OFFSET:        840 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       1044
  Y_GRB_POS:       1000
  BINNING_INDEX:   1
  IM_URL:          sw01297508000msuni0163.fits
  SUN_POSTN:         0.62d {+00h 02m 28s}   +0.27d {+00d 16' 04"}
  SUN_DIST:         66.93 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
  MOON_POSTN:      252.25d {+16h 49m 01s}  -27.68d {-27d 40' 46"}
  MOON_DIST:        64.14 [deg]
  MOON_ILLUM:      64 [%]
  GAL_COORDS:       57.11, -0.68 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      302.00, 41.74 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Processed Image.  
  COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
  COMMENTS:        The image has 2x2 binning (compression).  
  COMMENTS:        All 4 attachments are included.  
  

  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Fri 21 Mar 25 01:05:18 UT
  NOTICE_TYPE:     Swift-UVOT Image
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  POINT_RA:        295.063d {+19h 40m 15s} (J2000)
  POINT_DEC:       +21.044d {+21d 02' 38"} (J2000)
  ROLL:            99.011d
  IMG_START_DATE:  20755 TJD;    80 DOY;   25/03/21
  IMG_START_TIME:  2686.79 SOD {00:44:46.79} UT,   127.9 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     764210722
  X_OFFSET:        884 [pixels]
  Y_OFFSET:        840 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       1044
  Y_GRB_POS:       1000
  BINNING_INDEX:   1
  IM_URL:          sw01297508000msuni0163.fits
  SUN_POSTN:         0.62d {+00h 02m 28s}   +0.27d {+00d 16' 04"}
  SUN_DIST:         66.93 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
  MOON_POSTN:      252.25d {+16h 49m 00s}  -27.68d {-27d 40' 46"}
  MOON_DIST:        64.14 [deg]
  MOON_ILLUM:      64 [%]
  GAL_COORDS:       57.11, -0.68 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      302.00, 41.74 [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:     Fri 21 Mar 25 01:06:19 UT
  NOTICE_TYPE:     Swift-UVOT Source List
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  POINT_RA:        295.063d {+19h 40m 15s} (J2000)
  POINT_DEC:       +21.044d {+21d 02' 38"} (J2000)
  POINT_ROLL:      99.011d
  IMG_START_DATE:  20755 TJD;    80 DOY;   25/03/21
  IMG_START_TIME:  2898.84 SOD {00:48:18.84} UT,   340.0 [sec] since BAT Trigger Time
  FILTER:          7, U
  BKG_MEAN:        0.527
  N_STARS:         21
  X_OFFSET:        325 [pixels]
  Y_OFFSET:        281 [pixels]
  X_MAX:           1764 [pixels]
  Y_MAX:           1720 [pixels]
  DET_THRESH:      7
  PHOTO_THRESH:    3
  SL_URL:          sw01297508000msufc0339.fits
  SUN_POSTN:         0.62d {+00h 02m 28s}   +0.27d {+00d 16' 05"}
  SUN_DIST:         66.93 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
  MOON_POSTN:      252.26d {+16h 49m 03s}  -27.68d {-27d 40' 50"}
  MOON_DIST:        64.14 [deg]
  MOON_ILLUM:      64 [%]
  GAL_COORDS:       57.11, -0.68 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      302.00, 41.74 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Source List.  
  COMMENTS:        The Pointing RA,Dec,Roll values came from the 1st SrcList Notice.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Fri 21 Mar 25 01:06:34 UT
  NOTICE_TYPE:     Swift-UVOT Processed Source List
  TRIGGER_NUM:     1297508,   Seg_Num: 0
  POINT_RA:        295.063d {+19h 40m 15s} (J2000)
  POINT_DEC:       +21.044d {+21d 02' 38"} (J2000)
  POINT_ROLL:      99.011d
  IMG_START_DATE:  20755 TJD;    80 DOY;   25/03/21
  IMG_START_TIME:  2898.84 SOD {00:48:18.84} UT,   340.0 [sec] since BAT Trigger Time
  FILTER:          7, U
  BKG_MEAN:        0.527
  N_STARS:         21
  X_OFFSET:        325 [pixels]
  Y_OFFSET:        281 [pixels]
  X_MAX:           1764 [pixels]
  Y_MAX:           1720 [pixels]
  DET_THRESH:      7
  PHOTO_THRESH:    3
  SL_URL:          sw01297508000msufc0339.fits
  SUN_POSTN:         0.62d {+00h 02m 29s}   +0.27d {+00d 16' 05"}
  SUN_DIST:         66.93 [deg]   Sun_angle= 4.4 [hr] (West of Sun)
  MOON_POSTN:      252.26d {+16h 49m 03s}  -27.68d {-27d 40' 51"}
  MOON_DIST:        64.14 [deg]
  MOON_ILLUM:      64 [%]
  GAL_COORDS:       57.11, -0.68 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      302.00, 41.74 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Processed Source List.  
  COMMENTS:        If you have elected to receive attachments:  
  COMMENTS:        The uvot_catalog_srclist.fits.gz file does not exist; skipping the attachment.  
  

  
• GCN Circular #39795
  R. Hamburg (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
  "At 00:42:39.02 UT on 21 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250321A (trigger 764210564/250321030), which was also detected by Swift BAT (Gupta et al. 2025, GCN 39794). The Fermi GBM on-ground location is consistent with the Swift BAT position.
  The angle from the Fermi LAT boresight is 39 degrees.
  The GBM light curve shows one main pulse with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+7.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.83 +/- 0.20 and the cutoff energy, parameterized as Epeak, is 101 +/- 12 keV.
  The event fluence (10-1000 keV) in this time interval is (1.04 +/- 0.08)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.13 s in the 10-1000 keV band is 4.7 +/- 0.3 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 #39798
  K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team:
  Using 1.7 ks of XRT Photon Counting mode data starting 134 s after the BAT trigger on GRB 250321A (GCN Circ. 39794), an X-ray source was identified at a position of RA, Dec = 295.09873, 21.04146, which is equivalent to

  RA (J2000): 19h 40m 23.7s
  Dec (J2000): 21d 02′ 29.3″
  

  with an uncertainty of 4.2 arcsec.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #39799
  A. Kumar, S. Belkin, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. O'Neill, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration:
  The Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) observed the field of GRB 250321A, detected by Fermi/GBM (Fermi GBM Team, GCN 39793) and Swift/BAT (Gupta et al., GCN 39794). The position of the Swift/XRT counterpart (Page, GCN 39798) was covered by GOTO-North at 05:25:29 UT on 2025-03-21 (4.7 hours post-trigger). The observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
  Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using recent survey observations of the same pointings. No optical counterpart is detected in the Swift/XRT localisation region (Page, GCN 39798) down to a 3-sigma L-band limit of 19.6 mag (AB).
  Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
  GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
• GCN Circular #39801
  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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250321A ( Fermi GBM team, GCN 39793) errorbox 25226 sec after notice time and 25261 sec after trigger time at 2025-03-21 07:43:40 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 82 deg. The sun altitude is -37.1 deg.
  The galactic latitude b = -6 deg., longitude l = 56 deg.
  Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2818762
  We obtain a following upper limits.

  Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
  _________|_____________________|_____________________|____________________________________|_____|_______|_______|________
  
     25341 | 2025-03-21 07:43:40 |         MASTER-OAFA | (19h 30m 40.40s , +20d 25m 41.2s) |   C |   160 | 16.0 |        
     25537 | 2025-03-21 07:46:56 |         MASTER-OAFA | (19h 30m 47.85s , +20d 25m 03.0s) |   C |   160 | 16.4 |        
     25733 | 2025-03-21 07:50:11 |         MASTER-OAFA | (19h 30m 42.54s , +20d 24m 22.3s) |   C |   160 | 16.7 |        
     26355 | 2025-03-21 08:00:33 |         MASTER-OAFA | (19h 30m 43.53s , +20d 26m 11.7s) |   C |   160 | 16.4 |        
     27421 | 2025-03-21 08:19:20 |         MASTER-OAFA | (19h 30m 53.70s , +20d 27m 42.1s) |   C |    40 | 17.0 |        
     27431 | 2025-03-21 08:19:20 |         MASTER-OAFA | (19h 40m 32.05s , +20d 50m 27.7s) |   C |    60 | 16.6 |        
     27559 | 2025-03-21 08:20:37 |         MASTER-OAFA | (19h 30m 47.78s , +20d 27m 00.4s) |   C |   160 | 16.8 |        
     27569 | 2025-03-21 08:20:38 |         MASTER-OAFA | (19h 41m 30.19s , +20d 47m 56.2s) |   C |   180 | 16.7 |        
     27694 | 2025-03-21 08:23:53 |         MASTER-OAFA | (19h 30m 54.58s , +20d 27m 29.9s) |   C |    40 | 17.1 |        
  

  Filter C is a clear (unfiltred) band.
  The observation and reduction will continue. The message may be cited.
• GCN Circular #39802
  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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 250321A ( R. Gupta et al., GCN 39794) errorbox 27374 sec after notice time and 27401 sec after trigger time at 2025-03-21 08:19:20 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 78 deg. The sun altitude is -30.1 deg.
  The galactic latitude b = -1 deg., longitude l = 57 deg.
  Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2818736
  We obtain a following upper limits.

  Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
  _________|_____________________|_____|_______|______|________
  
     27432 |         MASTER-OAFA |   C |    60 | 16.6 |        
     27569 |         MASTER-OAFA |   C |   180 | 16.7 |        
  

  Filter C is a clear (unfiltred) band.
  The observation and reduction will continue. The message may be cited.
• GCN Circular #39814
  S. P. R. Shilling (Lancaster U.) and R. Gupta (NASA/GSFC) report on behalf of the Swift/UVOT team:
  The Swift/UVOT began settled observations of the field of GRB 250321A 128 s after the BAT trigger (Gupta et al., GCN Circ. 39794). No optical afterglow consistent with the XRT position (Page et al., GCN Circ. 39798) 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           128          278          147         >19.9
  white              128         4071          344         >20.6
  v                 4282         4482          197         >18.9
  b                 3667         5142          236         >20.0
  u                  340         5097          232         >19.4
  w1                4693         4892          197         >19.3
  m2                4487         4687          197         >19.2
  w2                4077         4277          197         >19.3
  

  The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 4.368 in the direction of the burst (Schlegel et al. 1998).
• GCN Circular #39820
  E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), M. A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
  We have analysed 6.8 ks of XRT data for the Swift-BAT-detected burst GRB 250321A, from 108 s to 39.4 ks after the Swift-BAT trigger. The data comprise 9 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. Using 1662 s of PC mode data and 3 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 295.09844, +21.04038 which is equivalent to:

  RA (J2000): 19h 40m 23.62s
  Dec(J2000): +21d 02' 25.4"
  

  with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position is 72 arcsec from the Swift-BAT position.
  The light curve can be modelled with a power-law decay with a decay index of alpha=1.13 (+0.11, -0.10).
  A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+1.3, -1.0). The best-fitting absorption column is 3.7 (+3.4, -2.2) x 10^22 cm^-2, in excess of the Galactic value of 1.1 x 10^22 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 7.3 x 10^-11 (2.4 x 10^-10) erg cm^-2 count^-1.
  A summary of the PC-mode spectrum is thus:

  Total column:	     3.7 (+3.4, -2.2) x 10^22 cm^-2
  Galactic foreground: 1.1 x 10^22 cm^-2
  Excess significance: 2.0 sigma
  Photon index:	     2.2 (+1.3, -1.0)
  

  If the light curve continues to decay with a power-law decay index of 1.13, the count rate at T+24 hours will be 6.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.0 x 10^-14 (1.6 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/01297508.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #39821
  R. Gupta (GSFC), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (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 250321A (trigger #1297508) (Gupta, et al., GCN Circ. 39794). The BAT ground-calculated position is RA, Dec = 295.100, 21.055 deg which is

     RA(J2000)  =  19h 40m 23.9s
     Dec(J2000) = +21d 03' 16.4"
  

  with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 24%.
  The mask-weighted BAT light curve shows a sharp peak at the trigger time, followed by a rapid decline. T90 (15-350 keV) is 6.21 +- 1.36 sec (estimated error including systematics).
  The time-averaged spectrum from T-0.14 to T+7.35 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.61 +- 0.19. The fluence in the 15-150 keV band is 6.7 +- 0.8 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T-0.16 sec in the 15-150 keV band is 3.2 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
  The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1297508