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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"
  1. GRB 250314A: Keck/NIRC2 J-band upper limit
  2. EP250226a/GRB 250226A: KAIT optical observations
  3. GRB 250321A: Fermi GBM Observation
  4. GRB 250321A: Swift detection of a burst
  5. GRB 250321A: Fermi GBM Final Real-time Localization
  6. GRB 250320B: Fermi GBM Final Real-time Localization
  7. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  8. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  9. GRB 250320A: Fermi GBM Final Real-time Localization
  10. Fermi GRB 250319B: Global MASTER-Net observations report
  11. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  12. GRB 250313A: GRBAlpha detection
  13. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  14. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  15. GRB 250319B: Fermi GBM Final Localization
  16. GRB 250319A: Fermi GBM Final Localization
  17. GRB 250317D: EIRSAT-1 GMOD Detection
  18. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  19. GRB 250314A: ATCA radio upper limits
  20. EP250302a: VLA observations
  21. GRB 250317B: OHP/T193 continued follow-up
  22. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  23. GRB 250317C: SVOM/GRM observation of a long burst
  24. GRB 250317B: Leavitt Observatory optical upper limit
  25. GRB 250309B/AT2025dws: further ATCA observations
  26. GRB 250317B: Mondy AZT-33IK Optical Observations
  27. GRB 250317C: AstroSat CZTI detection
  28. GRB 250317B: NOT optical observations suggest an optical plateau phase
  29. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  30. GRB 250317C: GECAM-B detection
  31. GRB 250317B: OHP/T193 optical observations
  32. Fermi trigger No 763933627: Global MASTER-Net observations report
  33. GRB250312A: Swift/UVOT Upper Limits
  34. GRB 250317B: REM optical/NIR observations
  35. GRB 250317B: Swift-XRT observations
  36. GRB 250316A: Swift/UVOT Upper Limits
  37. GRB 250314A: REM optical/NIR upper limits
  38. GRB 250316A: AbAO AS-32 Optical Upper Limit
  39. EP 250317B: Fading optical counterpart detection by LCO
  40. GRB 250316A: Swift-XRT afterglow detection
  41. GRB 250317B: LCO detection of the fading optical afterglow
  42. GRB 250317B: refined SVOM/MXT analysis
  43. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  44. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  45. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  46. GRB 250317B: SVOM detection of a burst
  47. GRB 250316A: Fermi GBM Observation
  48. GRB 250316A: Swift-XRT observations
  49. Fermi trigger No 763862734: Global MASTER-Net observations report
  50. GRB 250317A: Fermi GBM Final Real-time Localization
  51. Fermi GRB 250316A: Global MASTER-Net observations report
  52. GRB 250314A: SVOM/GRM analysis
  53. GRB 250316A: Swift ToO observations
  54. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  55. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  56. The EP-WXT trigger 01709132801 is likely a flaring star
  57. GRB 250316A: Fermi GBM Final Real-time Localization
  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 250312B: GRBAlpha detection
  63. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  64. GRB 250314A: Swift XRT Detection
  65. EP250315a: optical counterpart candidate detected by Gemini North
  66. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  67. EP250315a: Einstein Probe detection of an X-ray transient
  68. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  69. SVOM/MXT upper limit on GRB 250314A
  70. GRB 250314A: SVOM/VT upper limit
  71. GRB 250314A: NOT near-infrared candidate counterpart
  72. GRB 250313A: Fermi GBM Detection
  73. GRB 250313A: CALET Gamma-Ray Burst Monitor detection
  74. GRB 250312B: Fermi GBM Observation
  75. GRB 250313A: Swift-XRT observations
  76. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  77. Konus-Wind detection of GRB 250313A
  78. Konus-Wind detection of GRB 250308A
  79. GRB 250314A: SVOM detection of a burst
  80. EP250311a/GRB 250311A: Correction to EP-WXT detection time
  81. GRB 250313B: SVOM/GRM observation of a soft bright short burst
  82. GRB 250313A: SVOM/GRM observation of a bright long burst
  83. FRB 20250206A: Nondetection of Repeating Bursts from FRB 20250206A with FAST
  84. GRB 250313A: AstroSat CZTI detection of a bright long burst
  85. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  86. Fermi trigger No 763581136: Global MASTER-Net observations report
  87. GRB 250313A: Fermi-LAT detection
  88. GRB 250313A: Swift ToO observations
  89. EP250304a: Pan-STARRS r and i-band imaging and photometry
  90. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  91. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  92. Fermi GRB 250313A: Global MASTER-Net observations report
  93. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  94. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  95. GRB 250313A: Fermi GBM Final Real-time Localization
  96. The EP-WXT trigger 01709132551 is not a real source
  97. EP250304a: SVOM/VT optical observation
  98. EP250311a/GRB 250311A: EP-FXT follow-up observation
  99. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  100. EP250302a: Chandra X-ray Detection

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