Gamma-ray Burst 250828B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN/BACODINE POSITION NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 28 Aug 25 22:33:52 UT
  NOTICE_TYPE:     Swift-BAT GRB Position
  TRIGGER_NUM:     1345836,   Seg_Num: 0
  GRB_RA:          124.852d {+08h 19m 24s} (J2000),
                   125.144d {+08h 20m 34s} (current),
                   124.283d {+08h 17m 08s} (1950)
  GRB_DEC:         -17.388d {-17d 23' 17"} (J2000),
                   -17.470d {-17d 28' 12"} (current),
                   -17.230d {-17d 13' 49"} (1950)
  GRB_ERROR:       3.00 [arcmin radius, statistical only]
  GRB_INTEN:       2725 [cnts]    Image_Peak=171 [image_cnts]
  TRIGGER_DUR:     1.024 [sec] 
  TRIGGER_INDEX:   148     E_range: 25-100 keV
  BKG_INTEN:       16336 [cnts]
  BKG_TIME:        81203.77 SOD {22:33:23.77} UT
  BKG_DUR:         8 [sec]
  GRB_DATE:        20915 TJD;   240 DOY;   25/08/28
  GRB_TIME:        81217.85 SOD {22:33:37.85} UT
  GRB_PHI:         -152.09 [deg]
  GRB_THETA:        34.78 [deg]
  SOLN_STATUS:     0x3
  RATE_SIGNIF:     12.52 [sigma]
  IMAGE_SIGNIF:    9.25 [sigma]
  MERIT_PARAMS:     +1  +0  +0  +0  +2  +0 -100  +0 -74  +0 
  SUN_POSTN:       157.65d {+10h 30m 36s}   +9.36d {+09d 21' 33"}
  SUN_DIST:         41.85 [deg]   Sun_angle= 2.2 [hr] (West of Sun)
  MOON_POSTN:      216.72d {+14h 26m 53s}  -18.98d {-18d 58' 49"}
  MOON_DIST:        85.82 [deg]
  MOON_ILLUM:      29 [%]
  GAL_COORDS:      238.79, 10.47 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      132.29,-35.85 [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 = 207.45,-19.22 [deg].  
  

• red DSS finding chart ps-file
  
  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 28 Aug 25 22:38:28 UT
  NOTICE_TYPE:     Swift-BAT GRB Lightcurve
  TRIGGER_NUM:     1345836,   Seg_Num: 0
  GRB_RA:          124.852d {+08h 19m 24s} (J2000),
                   125.144d {+08h 20m 34s} (current),
                   124.283d {+08h 17m 08s} (1950)
  GRB_DEC:         -17.388d {-17d 23' 17"} (J2000),
                   -17.470d {-17d 28' 12"} (current),
                   -17.230d {-17d 13' 49"} (1950)
  GRB_DATE:        20915 TJD;   240 DOY;   25/08/28
  GRB_TIME:        81217.85 SOD {22:33:37.85} UT
  TRIGGER_INDEX:   148
  GRB_PHI:         -152.09 [deg]
  GRB_THETA:        34.78 [deg]
  DELTA_TIME:      32.00 [sec]
  TRIGGER_DUR:     1.024 [sec] 
  SOLN_STATUS:     0x3
  RATE_SIGNIF:     12.52 [sigma]
  IMAGE_SIGNIF:    9.25 [sigma]
  LC_URL:          sw01345836000msb.lc
  SUN_POSTN:       157.65d {+10h 30m 37s}   +9.36d {+09d 21' 29"}
  SUN_DIST:         41.85 [deg]   Sun_angle= 2.2 [hr] (West of Sun)
  MOON_POSTN:      216.76d {+14h 27m 01s}  -18.99d {-18d 59' 40"}
  MOON_DIST:        85.85 [deg]
  MOON_ILLUM:      29 [%]
  GAL_COORDS:      238.79, 10.47 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      132.29,-35.85 [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 = 207.45,-19.22 [deg].  
  

  
• GCN Circular #41581
  P. A. Evans (U Leicester), R. Gupta (NASA GSFC), J. A. Kennea (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
  At 22:33:37 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250828B (trigger=1345836). Swift could not slew to the burst due to an observing constraint. The BAT on-board calculated location is RA, Dec 124.852, -17.388 which is

     RA(J2000) = 08h 19m 24s
     Dec(J2000) = -17d 23' 17"
  

  with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 8 sec. The peak count rate was ~1700 counts/sec (15-350 keV), at ~0 sec after the trigger.
  Due to a Sun observing constraint, Swift cannot slew to the BAT position until 17:55 UT on 2025 September 07. There will thus be no XRT or UVOT data for this trigger before this time.
  We note that this GRB is coincident within one minute with a subthreshold Gravitational Wave trigger S250828ef, at 22:32:44 UT. However, this GW trigger is of low confidence, rated as 99% likely to be Terrestrial background noise.
  Burst Advocate for this burst is P. A. Evans (pae9 AT leicester.ac.uk). 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 #41589
  V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO), 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 250828B ( P. A. Evans et al., GCN 41581) errorbox 36970 sec after notice time and 36991 sec after trigger time at 2025-08-29 08:50:09 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 76 deg. The sun altitude is -27.3 deg.
  The galactic latitude b = 11 deg., longitude l = 239 deg.
  Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2978941
  We obtain a following upper limits.

  Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
  _________|_____________________|_____|_______|______|________
  
     37021 |         MASTER-OAFA |   C |    60 | 17.9 |        
     37101 |         MASTER-OAFA |   C |    60 | 18.0 |        
  

  Filter C is a clear (unfiltred) band.
  The observation and reduction will continue. The message may be cited.
• GCN Circular #41598
  M. J. Moss (GSFC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), P. A. Evans (U Leicester), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (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 250828B (trigger #1345836) (Evans et al., GCN Circ. 41581). The BAT ground-calculated position is RA, Dec = 124.867, -17.352 deg which is

     RA(J2000)  =  08h 19m 28.2s
     Dec(J2000) = -17d 21' 07.8"
  

  with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 64%.
  The mask-weighted light curve shows a complex structure. The main pulse starts and peaks at ~T0, and ends at ~T+5 s. In addition, there are some weak emission that starts prior to the main pulse at ~T-60 s and persists after the main pulse until ~T+60 s. T90 (15-350 keV) is 94.09 +- 32.03 sec (estimated error including systematics).
  The time-averaged spectrum from T-56.23 to T+76.66 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.13 +- 0.19. The fluence in the 15-150 keV band is 1.5 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+0.12 sec in the 15-150 keV band is 1.7 +- 0.2 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/1345836