GRB 240716A

Wen-Jun Tan,  Yong-Wei Dong, Jiang He, Yue Huang, Lu Li, Jiang-Tao Liu, Hao-Li Shi, Jian-Chao Sun, Chen-Wei Wang, Ping Wang, Bo-Bing Wu, Shao-Lin Xiong,  Li Zhang, Xiao-Yun Zhao, Shi-Jie Zheng, Shuang-Nan Zhang (IHEP)

report on behalf of the SVOM/GRM team:

During the commissioning phase, the SVOM/GRM was triggered by a long GRB 240716A at 2024-07-16T10:21:37.000 UT (T0) in-flight.

The real-time alert data and light curves produced were downlinked to the ground through the VHF system with low latency.

The light curve shows that this burst consists of a FRED-shape pulse with a duration of about 8 s, indicating that it is a long burst.

The GRM light curve can be found here:
http://www.bursthub.cn//admin/static/svgrb240716A.png

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.

The SVOM point of contact for this burst is: Wen-Jun Tan (IHEP)(tanwj@ihep.ac.cn)

Wen-Long Zhang, Shao-Lin Xiong, Shi-Jie Zheng, Yue Huang, Yan-Qiu Zhang, Wen-Jun Tan, Chen-Wei Wang, Peng Zhang report on behalf of the GECAM team:

GECAM-B was triggered in-flight by a long burst, GRB 240716A, at 2024-07-16T10:21:35.300 UTC (T0), which was also observed by SVOM/GRM (GCN # 36895). 

According to the realtime alert data downlinked through the BeiDou Navigation Satellite System (BDS), the GECAM-B light curve shows a long pulse with a total duration of ~8 sec (30-1020 keV). 

The GECAM-B in-flight location (J2000) is: 
Ra: 116.43 deg   
Dec: 46.57 deg
Err: 2.97 deg (1-sigma, statistical only)

The time-averaged spectrum of GECAM-B realtime data from about T0-0.5 to T0+3.5s could be adequately fit by a Band function with a fluence about 4.16E-6 erg/cm^2 in 20-1000 keV.

The GECAM-B light curve can be found here:
http://www.bursthub.cn//admin/static/gecamgrb240716A.png

We note that these results are based on realtime alert data and thus very preliminary. Refined analysis will be reported later.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).

GRB 240716A: Swift/BAT-GUANO localization skymap of a long burst

James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report: 

We announce a new data product from the NITRATES analysis run on BAT-GUANO data. NITRATES is now able to produce calibrated skymaps that describe the localization probability over the entire sky. These will apply to GRBs that are detected but for which arcminute precision localization is not feasible, due to either weak detection or origin outside the coded FOV (expected rate of ~a few per month).
Starting today these skymaps will be reported in lower latency, in the form of circulars as well as  GCN kafka notices under the topic "gcn.notices.swift.bat.guano". They can be distinguished from arcminute localized notices by their fields, see link to documentation below.

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Swift/BAT did not localize GRB 240716A onboard (T0: 2024-07-16 10:21:35.301 UTC, GECAM trig 408 / GCN 36896
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 , SVOM/GRM GCN 36895
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 ) 

The GECAM 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), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 28.5 in a 4.096 s analysis time bin, starting at T0 + 0.0 s. 

With a DeltaLLHOut of -30.1, NITRATES results are able to constrain the position of this burst to most likely be outside the coded field of view. 

See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. 

Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2024. in prep)

The 90% credible area is 249 deg2 and the 50% credible area is 61 deg2.
The integrated probability inside the coded field of view is ~0%. 

A plot of the probability skymap can be viewed here,
[https://guano.swift.psu.edu/trigger_report?id=742818129/#:~:text=Probability%20Skymap](https://guano.swift.psu.edu/trigger_report?id=742818129/#:~:text=Probability%20Skymap)

The probability skymap file can be downloaded from the link here,
https://guano.swift.psu.edu/files/742818129/0_n_PROBMAP

Instructions on how to read and manipulate this map can be found here,
https://guano.swift.psu.edu/documentation

More details about this burst can be found on the trigger report page here
https://guano.swift.psu.edu/trigger_report?id=742818129

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/