Gamma-ray Burst 250527C

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 May 25 14:03:02 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      46
TRIGGER_NUM:     770047117
GRB_RA:          338.133d {+22h 32m 32s} (J2000),
                 338.392d {+22h 33m 34s} (current),
                 337.626d {+22h 30m 30s} (1950)
GRB_DEC:         +51.900d {+51d 53' 60"} (J2000),
                 +52.031d {+52d 01' 53"} (current),
                 +51.642d {+51d 38' 32"} (1950)
GRB_ERROR:       32.53 [deg radius, statistical plus systematic]
GRB_INTEN:       48 [cnts/sec]
DATA_SIGNIF:     4.60 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20822 TJD;   147 DOY;   25/05/27
GRB_TIME:        50312.41 SOD {13:58:32.41} UT
GRB_PHI:          72.00 [deg]
GRB_THETA:        80.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.81
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      93%  GRB
2nd_MOST_LIKELY:   4%  Cyg X-1
DETECTORS:       0,1,1, 0,0,0, 0,0,0, 0,1,0, 0,0,
SUN_POSTN:        64.69d {+04h 18m 45s}  +21.40d {+21d 23' 51"}
SUN_DIST:         71.06 [deg]   Sun_angle= 5.8 [hr] (West of Sun)
MOON_POSTN:       70.99d {+04h 43m 58s}  +27.23d {+27d 14' 00"}
MOON_DIST:        70.37 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:      102.26, -5.31 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       10.12, 54.43 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250527582/quicklook/glg_lc_medres34_bn250527582.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 247.20,-6.45 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 May 25 14:16:08 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     770047117
GRB_RA:          286.950d {+19h 07m 48s} (J2000),
                 286.929d {+19h 07m 43s} (current),
                 286.989d {+19h 07m 57s} (1950)
GRB_DEC:         +68.650d {+68d 39' 00"} (J2000),
                 +68.691d {+68d 41' 28"} (current),
                 +68.569d {+68d 34' 07"} (1950)
GRB_ERROR:       22.79 [deg radius, statistical only]
DATA_SIGNIF:     4.80 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20822 TJD;   147 DOY;   25/05/27
GRB_TIME:        50312.41 SOD {13:58:32.41} UT
GRB_PHI:          83.00 [deg]
GRB_THETA:       107.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        64.70d {+04h 18m 47s}  +21.40d {+21d 23' 57"}
SUN_DIST:         84.87 [deg]   Sun_angle= 9.2 [hr] (West of Sun)
MOON_POSTN:       71.14d {+04h 44m 34s}  +27.25d {+27d 15' 11"}
MOON_DIST:        80.53 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       99.57, 23.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       25.65, 83.24 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250527582/quicklook/glg_lc_medres34_bn250527582.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_770047117.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 May 25 22:22:01 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     770047117
GRB_RA:          316.810d {+21h 07m 14s} (J2000),
                 317.002d {+21h 08m 00s} (current),
                 316.433d {+21h 05m 44s} (1950)
GRB_DEC:         +54.130d {+54d 07' 48"} (J2000),
                 +54.233d {+54d 13' 60"} (current),
                 +53.928d {+53d 55' 40"} (1950)
GRB_ERROR:       11.19 [deg radius, statistical only]
GRB_DATE:        20822 TJD;   147 DOY;   25/05/27
GRB_TIME:        50312.41 SOD {13:58:32.41} UT
GRB_PHI:          83.00 [deg]
GRB_THETA:        87.00 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:        65.04d {+04h 20m 09s}  +21.45d {+21d 27' 13"}
SUN_DIST:         82.63 [deg]   Sun_angle= 7.2 [hr] (West of Sun)
MOON_POSTN:       76.76d {+05h 07m 03s}  +27.87d {+27d 52' 19"}
MOON_DIST:        82.94 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:       93.75,  4.49 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      353.91, 64.56 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250527582/quicklook/glg_lc_medres34_bn250527582.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250527582/quicklook/glg_locplot_all_bn250527582.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice has human-in-the-loop processing.

GCN Circular #40563
James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 250527C onboard (T0: 2025-05-27T13:58:32.41 UTC, Fermi Trig 770047117).
The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), detects the burst in a 8.192 s analysis time bin starting at T0 - 4.096 s with a sqrt(TS) of 11.6. An arcminute localization is found with DeltaLLHOut of 29.5 and a DeltaLLHPeak of 17.4.
See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
The BAT position is RA, Dec = 319.633, 52.737 deg which is
```
   RA(J2000)  = 21h 18m 31.92s
   Dec(J2000) = 52d 44’ 13.2″
```
with an estimated uncertainty of 5 arcmin radius.
More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=770047148
XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars.
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular #40564
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT-detected event GRB 250527C. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021843 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Swift/BAT event. 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 #40574
N. Klingler (UMBC / NASA-GSFC / CRESST II) reports on behalf of the Swift/UVOT team:
Swift/UVOT has performed observations of GRB 250527C centered on the BAT position, RA, Dec = 21h 18m 31.92s, +52d 44' 13.2" (= 319.633, 52.737 deg; 90% uncertainty of 5 arcmin) (DeLaunay et al.; GCN 40563). UVOT collected 4536 s of data between 96 ks and 113 ks post-trigger, using the White filter.
No uncatalogued/transient sources are detected, with an approximate 3 sigma upper limit > 22.56 (AB) in the 90% BAT localization region.
For the X-ray sources detected by XRT (https://www.swift.ac.uk/ToO_GRBs/00021843/): sources 3, 4, and 6 fall outside the UVOT field of view. XRT source 2 is not detected. XRT source 1 is a star: TYC 3953-1190-2. XRT 5 has an optical counterpart (AB mag 17.99 +/- 0.07), but it is seen in archival DSS images and thus does not appear to be a transient.
No correction has been made for the expected Galactic extinction due to the reddening of E(B-V) = 3.43 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #40653
N. Pankov (HSE, IKI), S. Nazarov (CrAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 250527C detected by Fermi/GBM (Trigger 770047117) and further localized by Swift/BAT-GUANO (Delaunay et. al, GCN 40563). The field has also been observed by Swift/XRT (Evans, GCN 40564), and Swift/UVOT (Klingler, GCN 40574). Our observations were carried out using the Sintez-Newton 0.36-meter telescope installed at the Crimean Astrophysical Observatory (CrAO). The series of images has taken in the R-filter. We do not detect candidate transients in comparison with USNO-B1.0, and PS1 catalogs in the stacked image of 22*120 sec. Particularly, we were searching for candidates inside localization circles of X-Ray sources provided in (Evans, GCN 40564). The preliminary upper limit is given below:
```
Date       UTstart   T-T0   Exposure Filter OT  Err     UL
                              (n*T)                  (3-sigma)
2025-05-28 23:46:57 1.42390  22*120     R   n/d n/d    19.1
```
The photometry was calibrated using nearby USNO-B1.0 stars (R2 magnitudes) and has not been corrected for the Galactic extinction.

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Jochen Greiner, last update: 09-Jun-2025 [Disclaimer]