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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: SVOM/GRM analysis
  2. GRB 250316A: Swift ToO observations
  3. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  4. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  5. The EP-WXT trigger 01709132801 is likely a flaring star
  6. GRB 250316A: Fermi GBM Final Real-time Localization
  7. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  8. GRB 250314A: EP-FXT afterglow detection
  9. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  10. GRB 250314A: Swift/UVOT Upper Limits
  11. GRB 250312B: GRBAlpha detection
  12. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  13. GRB 250314A: Swift XRT Detection
  14. EP250315a: optical counterpart candidate detected by Gemini North
  15. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  16. EP250315a: Einstein Probe detection of an X-ray transient
  17. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  18. SVOM/MXT upper limit on GRB 250314A
  19. GRB 250314A: SVOM/VT upper limit
  20. GRB 250314A: NOT near-infrared candidate counterpart
  21. GRB 250313A: Fermi GBM Detection
  22. GRB 250313A: CALET Gamma-Ray Burst Monitor detection
  23. GRB 250312B: Fermi GBM Observation
  24. GRB 250313A: Swift-XRT observations
  25. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  26. Konus-Wind detection of GRB 250313A
  27. Konus-Wind detection of GRB 250308A
  28. GRB 250314A: SVOM detection of a burst
  29. EP250311a/GRB 250311A: Correction to EP-WXT detection time
  30. GRB 250313B: SVOM/GRM observation of a soft bright short burst
  31. GRB 250313A: SVOM/GRM observation of a bright long burst
  32. FRB 20250206A: Nondetection of Repeating Bursts from FRB 20250206A with FAST
  33. GRB 250313A: AstroSat CZTI detection of a bright long burst
  34. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  35. Fermi trigger No 763581136: Global MASTER-Net observations report
  36. GRB 250313A: Fermi-LAT detection
  37. GRB 250313A: Swift ToO observations
  38. EP250304a: Pan-STARRS r and i-band imaging and photometry
  39. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  40. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  41. Fermi GRB 250313A: Global MASTER-Net observations report
  42. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  43. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  44. GRB 250313A: Fermi GBM Final Real-time Localization
  45. The EP-WXT trigger 01709132551 is not a real source
  46. EP250304a: SVOM/VT optical observation
  47. EP250311a/GRB 250311A: EP-FXT follow-up observation
  48. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  49. EP250302a: Chandra X-ray Detection
  50. GRB 250312A: Swift-XRT refined Analysis
  51. Fermi Gamma-ray Burst Monitor trigger 763509110/250312911 is not a GRB
  52. Fermi trigger No 763509110: Global MASTER-Net observations report
  53. Fermi GRB 250312B: Global MASTER-Net observations report
  54. GRB 250312A: Enhanced Swift-XRT position
  55. GRB 250312B: Fermi GBM Final Localization
  56. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  57. GRB 250226B: Fermi GBM Observation
  58. Swift GRB 250312A: Global MASTER-Net observations report
  59. GRB 250302A: Fermi GBM Observation
  60. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  61. GRB 250312A: Swift detection of a burst
  62. GRB 241213A: VIRT Optical Upper Limit
  63. GRB 241228A: VIRT Optical Upper Limit
  64. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  65. GRB 250223B: Fermi GBM Observation
  66. GRB 250311A: Swift-XRT observations
  67. GRB 250228A: Fermi GBM Observation
  68. GRB 250309B: 1.3m DFOT Optical observations
  69. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  70. EP250311a: Global MASTER-Net observations report
  71. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  72. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  73. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  74. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  75. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  76. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  77. GRB 250309B: PRIME near-infrared detection
  78. EP250304a: Chandra detection
  79. GRB 250225B: Swift-BAT refined analysis
  80. GRB 250311A/EP250311a: TRT optical upper limit
  81. IceCube-250309A: MITSuME Akeno and Seimei/TriCCS optical observations
  82. GRB 250311A: Tiled Swift observations
  83. EP250311a/GRB 250311A: EP-WXT detection
  84. GRB 250308A: CALET Gamma-Ray Burst Monitor detection
  85. GRB 250311B: SVOM detection of a burst
  86. GRB 250309B: SVOM/VT optical observation
  87. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  88. The EP-WXT trigger 01709132425 is not a real source
  89. GRB 250309B / AT2025dws: further SAO RAS optical observations
  90. IceCube-250309A: Upper limits from Fermi-GBM Observations
  91. EP250308a: 1.6m Mephisto optical upper limits
  92. Konus-Wind detection of GRB 250309B
  93. GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
  94. IPN triangulation of GRB 250308A (short)
  95. IPN triangulation of GRB 250309B
  96. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  97. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  98. GRB 250309B: Swift-XRT refined Analysis
  99. GRB 250309B / IceCube-250309A: GECAM-B observations
  100. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898

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