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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

24754 results found.

  1. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  2. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  3. GRB 250320B: Fermi GBM Observation
  4. EP250321a: Xinglong 216 decaying optical observations
  5. GRB 250321A: Swift-BAT refined analysis
  6. GRB 250321A: Swift-XRT refined Analysis
  7. EP 250321A: Optical counterpart detection by LCO.
  8. EP250321a: Kinder optical follow-up observations
  9. GRB 250321A: Swift/UVOT Upper Limits
  10. GRB 250320B: SVOM/GRM observation of a long burst
  11. EP250321a: LCO optical counterpart detection
  12. EP250321a: Swift-XRT detection of an X-ray source
  13. EP250321A: COLIBRÍ Optical Observations
  14. GRB 250320B: AstroSat CZTI detection
  15. EP250321a: REM optical/NIR afterglow detection
  16. EP250321a: TRT optical counterpart detection
  17. Swift GRB 250321A: Global MASTER-Net observations report
  18. EP250321a: Einstein Probe detection of an X-ray transient
  19. GRB 250321A: GOTO optical upper limits
  20. GRB 250314A: Keck/NIRC2 J-band upper limit
  21. EP250226a/GRB 250226A: KAIT optical observations
  22. GRB 250321A: Fermi GBM Observation
  23. GRB 250321A: Swift detection of a burst
  24. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  25. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  26. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  27. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  28. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  29. GRB 250317D: EIRSAT-1 GMOD Detection
  30. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  31. GRB 250314A: ATCA radio upper limits
  32. GRB 250317B: OHP/T193 continued follow-up
  33. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  34. GRB 250317C: SVOM/GRM observation of a long burst
  35. GRB 250317B: Leavitt Observatory optical upper limit
  36. GRB 250317B: Mondy AZT-33IK Optical Observations
  37. GRB 250317B: NOT optical observations suggest an optical plateau phase
  38. GRB 250317C: GECAM-B detection
  39. GRB 250317B: OHP/T193 optical observations
  40. GRB250312A: Swift/UVOT Upper Limits
  41. GRB 250317B: REM optical/NIR observations
  42. GRB 250317B: Swift-XRT observations
  43. GRB 250316A: Swift/UVOT Upper Limits
  44. GRB 250314A: REM optical/NIR upper limits
  45. GRB 250316A: AbAO AS-32 Optical Upper Limit
  46. EP 250317B: Fading optical counterpart detection by LCO
  47. GRB 250316A: Swift-XRT afterglow detection
  48. GRB 250317B: LCO detection of the fading optical afterglow
  49. GRB250317B: SVOM/VT detection of an optical candidate from VHF data
  50. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  51. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  52. GRB 250317B: SVOM detection of a burst
  53. GRB 250316A: Fermi GBM Observation
  54. GRB 250316A: Swift-XRT observations
  55. GRB 250314A: SVOM/GRM analysis
  56. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  57. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  58. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  59. GRB 250314A: EP-FXT afterglow detection
  60. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  61. GRB 250314A: Swift/UVOT Upper Limits
  62. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  63. GRB 250314A: Swift XRT Detection
  64. EP250315a: optical counterpart candidate detected by Gemini North
  65. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  66. EP250315a: Einstein Probe detection of an X-ray transient
  67. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  68. SVOM/MXT upper limit on GRB 250314A
  69. GRB 250314A: SVOM/VT upper limit
  70. GRB 250314A: NOT near-infrared candidate counterpart
  71. GRB 250313A: Fermi GBM Detection
  72. GRB 250312B: Fermi GBM Observation
  73. GRB 250313A: Swift-XRT observations
  74. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  75. GRB 250314A: SVOM detection of a burst
  76. GRB 250313A: AstroSat CZTI detection of a bright long burst
  77. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  78. GRB 250313A: Fermi-LAT detection
  79. EP250304a: Pan-STARRS r and i-band imaging and photometry
  80. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  81. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  82. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  83. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  84. GRB 250312A: Swift-XRT refined Analysis
  85. GRB 250312A: Enhanced Swift-XRT position
  86. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  87. GRB 250226B: Fermi GBM Observation
  88. GRB 250302A: Fermi GBM Observation
  89. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  90. GRB 250312A: Swift detection of a burst
  91. GRB 241213A: VIRT Optical Upper Limit
  92. GRB 241228A: VIRT Optical Upper Limit
  93. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  94. GRB 250311A: Swift-XRT observations
  95. GRB 230509B: 1.3m DFOT Optical observations
  96. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  97. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  98. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  99. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  100. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB

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