GRB 260607B

Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260607B which was also detected by  Fermi GBM (Fermi GBM Team, GCN Circ. 44859
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 ), Fermi LAT (Airasca et. al. , GCN Circ. 44860
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 ).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-07 13:19:41.91 UTC. The measured peak count rate associated with the burst is 508 (+45, -30) counts/s above the background in the combined data of all quadrants, with a total of 8523 (+313, -323) counts. The local mean background count rate was 280 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 45.8 (+0.2, -0.6) s. 

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.The light curve showed multiple peaks of emission with the strongest peak at 2026-06-07 13:19:41.36 UTC. The measured peak count rate associated with the burst is 4613 (+124, -120) counts/s above the background in the combined data of all quadrants, with a total of 79352 (+766, -730) counts. The local mean background count rate was 1278 (+4, -5) counts/s. We measure a T90 of 45.8 (+0.1, -0.1) s from the cumulative Veto light curve.

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI data products like interactive and downloadable light curves for this GRB can be found at:
https://astrosat.iucaa.in/cift/cift_products/ET20260607T131928/ET20260607T131928_details.html

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb

E. Neights (GWU, NASA GSFC) and E. Palafox (INAOE-Mexico) report on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 13:19:28.70 UT on 07 June 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260607B (trigger 802531173/260607555),
which was also detected by Fermi LAT (Holzmann Airasca et al. 2026, GCN 44860
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 ).
The Fermi GBM on-ground location is consistent with the Fermi LAT position.

The angle from the Fermi LAT boresight is 72 degrees.

The GBM light curve consists of multiple emission episodes, with a duration (T90)
of about 47 s (50-300 keV). The time-averaged spectrum
from T0+2.9 to T0+57.1 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.92 +/- 0.004 and the cutoff energy,
parameterized as Epeak, is 728 +/- 2 keV.

The event fluence (10-1000 keV) in this time interval is
(2.999 +/- 0.006)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+53 s in the 10-1000 keV band is 66.9 +/- 0.5 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/"

A. Holzmann Airasca (UniTrento and INFN Bari), R. Gupta (NASA/GSFC) and N. Di Lalla (Stanford University) report on behalf of the Fermi-LAT team:

At 13:19:28.70 UT on June 7th, 2026 Fermi-LAT detected high-energy emission from GRB 260607B, which was also detected by Fermi-GBM (trigger 802531173/260607555, GCN #44859
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 ).

The best LAT on-ground location is found to be

RA, Dec = 54.68, 30.45 (J2000)

with an error radius of 0.40 deg (90 % containment, statistical error only).

This was 72 deg from the LAT boresight at the time of the trigger.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 0 - 1.2 ks after the GBM trigger is (2.22 ± 0.50)E-5 ph/cm2/s. The estimated photon index above 100 MeV is -1.98 ± 0.15. The highest energy photon has an energy of 4.7 GeV and occurs at 120 s after trigger time.

The Fermi-LAT point of contact for this burst is Niccolò Di Lalla (niccolo.dilalla@stanford.edu).

The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

The Fermi GBM team reports the detection of a likely LONG GRB

"At 13:19:28.70 UT on 07 June 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260607B (trigger 802531173/260607555).
This trigger was initially classified as Distant Particles by the flight software,
but is in fact a GRB.

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 55.11, Dec = 26.90 (J2000 degrees, equivalent to J2000 +03h 40m, +26d 54'),
with a statistical uncertainty of 1.00 degree.

The angle from the Fermi LAT boresight is 68 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607555/quicklook/glg_skymap_all_bn260607555.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607555/quicklook/glg_healpix_all_bn260607555.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260607555/quicklook/glg_lc_medres34_bn260607555.gif"